Hand your friend a +1 weapon
I do not believe there is a compelling optimization reason (ignoring character flavor) to regularly use different weapons. In combat, an action is simply too important to waste. It gets worse if you want to switch from sword and board to two-handed - you need an action to doff your shield and a separate action to summon your new weapon. Out of combat, weapon switching is typically either mechanically suboptimal (using a one-handed weapon when you have the Great Weapon Master feat) or pointless (switching from a longsword to a warhammer). Rarely will enemies be resistant or vulnerable to a specific mundane damage type.
That said, you know who uses a variety of weapons - your party. What if you made them more awesome?
- Take the Improved Pact Weapon Eldritch Invocation (XGtE, p. 56). This makes your pact weapons +1 and allows you to also conjure shortbows, longbows, light crossbows, or heavy crossbows. (You don't have to take this if you don't want to use non-PHB sources, but without it you are restricted to melee weapons. Additionally, the weapon does not have a +1 bonus, but will still bypass resistance to nonmagical weapons.)
- Determine who in your party doesn't have a magic weapon yet.
- Pick a different party member each day (or each encounter) and summon a pact weapon (outside of combat) in the form of a weapon that they use. This allows you to use your unique ability to summon a variety of weapons while keeping everyone happy. With all melee weapons and common ranged weapons to choose from, you should be able to give everyone a turn. The Pact of the Blade feature explicitly grants you proficiency with the weapon, but does not restrict others from using it if they already have proficiency with the chosen weapon type.
- Stay relatively close to your ally. The weapon disappears if it is more than 5 feet away from you for 1 minute or more. If you need to be separated for longer than that, just resummon the weapon using an action whenever you meet up again.
- In combat, you won't need to worry about positioning. In my experience, a typical combat in 5e lasts 2-5 rounds (30 seconds or less), so the pact weapon is in no danger of vanishing. On rare occasions, summoning a different +1 weapon (making the first one disappear) will be worth spending an action on in combat. Against flying enemies, it may be worth getting rid of a +1 greatsword on the barbarian for a +1 longbow on the ranger.
Some math
Unless otherwise noted, the following builds assume a level 5 PC with a 16 attack stat; any feats are taken at level 4. Damage is calculated vs an AC 16 enemy. In my experience, the bonus action attack from Great Weapon Master triggers on 1/4 to 1/3 of rounds. This damage is not included in the single round calculations.
- Great Weapon Master (GWM) Barbarian: 23.8 DPR (attacks recklessly for advantage, is raging, no magic weapon)
- Polearm Master (PAM) Warlock: 22.1 DPR with Hexblade's Curse up (only deals 16.1 damage on round 1), 16.0 DPR without (+1 weapon from Improved Pact Weapon on both)
- Eldritch Blast (EB) Warlock: 16.1 DPR (Agonizing Blast [PHB, p. 110], +2 CHA at level 4, Hex)
Let's look at the combined damage of a Great Weapon Master barbarian and one of two different warlocks. The barbarian has a +1 weapon from the Eldritch Blast warlock, but not from the Polearm Master one. Damage is averaged over 3 rounds (the bulk of a fight). I assume GWM's bonus attack triggers on the third round. I also assume that the melee warlock uses Eldritch Smite on the third round.
First, versus an enemy without resistances:
GWM+PAM:
- GWM Barb: 27.8 DPR = (23.8 + 23.8 + 35.7) / 3 rounds
- PAM Lock: 26.1 DPR = (16.1 + 22.1 + 40.1) / 3 rounds
- Total: 53.9 DPR
GWM+EB:
- GWM Barb: 32.6 DPR = (27.9 + 27.9 + 41.9) / 3 rounds
- EB Lock: 16.1 DPR = (16.1 + 16.1 + 16.1) / 3 rounds
- Total: 48.7 DPR (-10% DPR)
Without resistances, the Polearm Master warlock's extra DPS makes up for the barbarian's damage loss from not having a +1 to hit. How would they fare against an enemy with resistance to nonmagical weapons?
GWM+PAM with resist:
- GWM Barb: 13.9 DPR = ((23.8/2) + (23.8/2) + (35.7/2)) / 3 rounds
- PAM Lock: 26.1 DPR = (16.1 + 22.1 + 40.1) / 3 rounds
- Total: 40.0 DPR
GWM+EB with resist:
- GWM Barb: 32.6 DPR = (27.9 + 27.9 + 41.9) / 3 rounds
- EB Lock: 16.1 DPR = (16.1 + 16.1 + 16.1) / 3 rounds
- Total: 48.7 DPR (+22% DPR)
The minor decrease in warlock DPR is worth the major increase they can provide to the barbarian.
So is it any good?
To get the most out of giving away your pact weapon, you really should focus on Eldritch Blast instead of melee, at least in the early-mid levels.
The pros
- Significantly better (+22% DPR) against enemies with resistance to nonmagical weapons.
- Only requires 2 invocations: Improved Pact Weapon and Agonizing Blast. After those, you can pick a couple utility or flavor invocations without feeling suboptimal.
- Actually benefits from your ability to conjure any weapon.
- Doesn't require a feat - you can get +2 CHA or take a flavor feat like Actor (PHB, p. 165).
- You don't have to go Hexblade. Any of the patrons work well with this build, though only Hexblade lets you change your mind and convert to melee later on.
- Your party will love you. I know this isn't a tangible benefit, but people love it when you give them stuff. This build lets you do that multiple times per day. For bonus points, let your allies make design requests; after all, you "choose the form that this melee weapon takes each time you create it".
The cons
- Slightly worse (-10% DPR) against enemies without resistance to nonmagical weapons.
- Doesn't involve you using the variety of weapons you summon, unless you convert to melee later on.
- A GWM barbarian is the best case ally for this build. If your party doesn't have any big hitters (barbarian, rogue, PAM, GWM, or Sharpshooter), you might be better off hitting things yourself.
- If your DM is overly-generous with magic items (or at higher levels where they are commonly found), your weapon summoning doesn't really provide any benefit. If you want to hedge your bets here, you can go Hexblade - use Eldritch Blast until no one needs a magic item, then swap out Agonizing Blast for Thirsting Blade on your next level up.
Example build
Pretty much any Eldritch Blast-based warlock build will work here, but I will assume that you want to hedge your bets with Hexblade and convert to melee later. All spells are from the PHB unless otherwise noted.
- Base stats after racials (level 1): 16 CHA, 14-16 CON, 14 DEX. Optimally play a variant human and take the Resilient feat (PHB, p. 168) for CON save proficiency. Most of your warlock spells are concentration and you don't have enough spell slots to waste re-casting them if you lose concentration by failing a CON save.
- By Level 4, you should be a Hexblade Pact of the Blade with Improved Pact Weapon and Agonizing Blast. Raise your CHA by +2 with your first ASI, or take a flavorful feat. Use a shield in one hand and an arcane focus in the other. Get the heaviest medium armor you can - eventually AC 19 with half-plate and a shield. Spells: hellish rebuke, hex, invisibility, shatter, and suggestion.
- Level 5: take a flavorful invocation, like Mask of Many Faces (PHB, p. 111). If none appeal to you, take Repelling Blast (PHB, p. 111) to push enemies into hazards (like hunger of hadar) or out of reach. Spells: learn hypnotic pattern and swap out shatter for hunger of hadar.
- Level 6: Spells: learn counterspell.
- Level 7: take Sculptor of Flesh (PHB, p. 111) for 1/day polymorph. Spells: learn banishment and swap out suggestion for dimension door.
- Level 8: most of your party has magic weapons by now, so it's time to convert to melee. (You can postpone this until level 12, if you want.) Take the Polearm Master feat. Swap out Agonizing Blast for Thirsting Blade. Spells: learn shadow of moil (XGtE, p. 164; sub mirror image for PHB-only) and swap out hex for elemental weapon. Use a quarterstaff+shield if you want to be tanky, or a glaive if you want reach and more damage.
("Drop hex? Are you crazy?" I know, I know, but consider this: PAM lets you attack with a bonus action and hex takes a bonus action to cast and to move to a new enemy. Besides, adding elemental weapon means you can still give out a magic weapon to an ally. Next level, you can give out a +2 to hit +2d4 damage weapon!)
- Level 9: Take Eldritch Smite. Consider swapping out the invocation you took at Level 5 for Whispers of the Grave (at-will speak with dead; PHB, p. 111) or Ghostly Gaze (1/rest see through walls; XGtE, p. 56). Spells: learn scrying and swap out hunger of hadar for synaptic static (XGtE, p. 167; sub cone of cold for PHB-only).
- Level 10: No real choices here, since you don't get a new spell or invocation. If there is a spell you find yourself not using, swap it out here.
- Level 11: Three spell slots - now we're talking! Note that you learn a new 1st-5th level spell in addition to gaining your first Mystic Arcanum. Mystic Arcanum: take mental prison (XGtE, p. 161; sub conjure fey for PHB-only) if you want damage/control, or scatter (XGtE, p. 164; sub true seeing or mass suggestion) if you want utility. You want to pick something here that you will use every day; you can't upcast using your Mystic Arcanum (since they have no slots), and you can't ever switch them out. Choose wisely! Spells: learn hold monster.
- Level 12: Raise your CHA by +2, or take the Great Weapon Master feat. Take Lifedrinker (PHB, p. 111). (If you chose not to switch over to melee before, now is the time.)
From then on out, your build is complete - take whatever suits you when you get there. For Mystic Arcanum, forcecage (no-save hard control), glibness (basically never fail a CHA check, including counterspell checks), and foresight (be an unstoppable melee machine) are great picks. If you delay (or decide against) converting to melee, just keep hex and don't swap to the other melee invocations.
Conclusion
Overall, this build probably starts slightly worse than a pure melee warlock or a pure EB warlock; however, you shouldn't ever feel behind the curve in a group of new players. After considering the options, I believe that handing off your pact weapon is the most effective way to actually use your ability to summon different weapons.
A footnote on things that don't work:
The designers (either by accident or intent) prevented most of the invocations from applying to someone else wielding your pact weapon. Lifedrinker, Thirsting Blade, and Eldritch Smite work when you do something with your pact weapon. Improved Pact Weapon is the only one that affects the weapon itself and thus works.
A footnote on Dual Wielding vs Polearm Master:
Without the fighting style Two Weapon Fighting (from dipping a level into fighter, for example), you can't add your ability modifier to the off-hand attack while dual wielding. (Polearm Master's bonus action attack doesn't have this limitation.) A Hexblade can use CHA for both their pact weapon and another weapon, but only your pact weapon will benefit from Improved Pact Weapon (gaining a +1 bonus) and, more importantly, Lifedrinker (gaining +CHA damage on each hit).
Feats are taken at level 8. Calculated vs an AC 16 enemy. I am ignoring Hexblade's Curse, since it affects both styles equally.
- Warlock 9, PAM, +1 glaive: 20.6 DPR
- Warlock 9, PAM, +1 quarterstaff: 17.6 DPR (and +2 to AC)
- Warlock 9, DW, +1 longsword & longsword: 16.9 DPR (and +1 to AC)
- Warlock 8 / Fighter 1, DW, +1 longsword & longsword: 19.5 DPR (and +1 to AC; can't cast 5th level spells yet)
(I used this AnyDice script for these calculations. The Summary tab is the best way to look at the data.)
I had to compare these at Level 9 to give the Fighter dip a chance to catch up. Even with a dip into fighter (delaying your spell progression), the Polearm Master wins out. Without it, even quarterstaff + shield wins. If you also find a +1 weapon for your off-hand, dual wielding barely breaks even (but does have a +1 to AC). The situation is worse once Lifedrinker comes into play at Warlock 12.
- Warlock 13, PAM, +1 glaive: 37.9 DPR
- Warlock 13, PAM, +1 quarterstaff: 34.5 DPR (and +2 to AC)
- Warlock 12 / Fighter 1, DW, +1 longsword & +1 longsword: 33.9 DPR (and +1 to AC; can't cast 7th level spells yet)
Finally, none of this takes into account Polearm Master's reaction attack when someone enters your reach.
Best Answer
They have not been specified for PC races.
While the statistics for draconians as monsters are included in Fizban's Treasury of Dragons, there are no rules for playing draconians as a variant of the dragonborn PC race. Fizban's does include more options for PC dragonborn, but all of them include breath weapons.