Brief backstory here, since I feel like Palalock gets enough of a backlash that I want to justify it. My group are longtime 3.5/Pathfinder players dipping our toes into 5e for the first time; we're playing the Tomb of Annihilation adventure from FR.
I am the party's primary frontline fighter, so I want to synergize abilities and feats to lockdown large sections of the battlefield and deal damage using Divine Smite and OAs, with some blasting for when melee isn't an option.
I'm playing a Half-Elf, background Faction Agent for Order of the Gauntlet. I've decided that I want to go Vengeance/Archfey. Father was an Eladrin, mother was a human priestess for one of the temples that formed the OotG (Order of the Gilded Eye, perhaps? I'll admit, the original Neverwinter Nights biases me against them a bit). I think Vengeance works for covering the … well, cliche at it ls let's just call it the darker side of the Order, particularly coming from the Helmites and Hoar-devotees. Archfey Warlock works on two levels thematically. The character having mostly been raised among humans, wanting to reach out and try to reconnect with a part of his heritage that hasn't been very prominent in his upbringing. Combined with Vengeance, you get a character that makes contact with Fey forces, gets excited about discovering a new part of him that he had never really known about before, and accepts a deal that can help him meet out justice. Of course, in his excitement and his rush, he doesn't -really- understand the full ramifications of what he's done, potentially opening up some interesting tensions between the Paladin oath and Fey pact later on. There's a bit of a Green Knight flavor there, even without going full hippie Oath of the Ancients.
There are three potential build combinations I'm looking at.
Starting stat block is 16 STR, 10 DEX, 14 CON, 10 WIS, 10 INT, 16 CHA. Wielding a Glaive, with the intent of grabbing Polearm Master and Sentinel.
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18 Paladin/2 Warlock
PROS: Bare minimum necessary to gain access to Invocations, plus two rechargeable Lvl 1 slots for 2d8 Smiting. Keeps the lvl 18 Aura Improvements for a Paladin (not going to come up in this campaign but we may continue on with these characters), and gets a 2nd 5th-level spell slot.
CONS: No capstone Oath feature, and losing an ASI means either STR or CHA is going to have to stay at 16 while the other gets boosted to 20. Figure this can be mitigated by getting my hands on a Belt of Giant's Strength and using the ASI's on CHA. -
17 Paladin/3 Warlock
PROS: Warlock spells slots are now level 2, meaning rechargeable 3d8 Smiting. Also gives access to Darkness spell, for tasty, tasty synergy with Polearm Master/Sentinel/Devil's Sight invocation. Pact Boon is a pretty secondary benefit, but it also gives access to these. Leaning towards Pact of the Chain, as Tome mainly shines at higher levels and I'm not interested in the Shillelagh/Bladelock build.
CONS: Gives up the 30ft range on the Paladin's Auras. Still losing an ASI. Currently what I am leaning towards the most. -
Paladin 16/Warlock 4
PROS: Gets an ASI/Feat back, meaning 20 STR/18 CHA or vice versa, or also getting the Resilient or War Caster feats (tasty proficiency in CON checks in general, which helps with Concentration, or specifically buffing Concentration checks made when taking damage and giving some excellent synergy with Sentinel and Polearm Master). Also gives an extra Warlock cantrip and spell known. Woo, I guess?
CONS: No 5th level Paladin spells. As Divine Smite bonuses cap out at the 4th level, this isn't terrible, but there are some nice 5th level spells. Holy Weapon and Banishing Smite are great, and Vengeance Paladin also gets access to Hold Monster.
I figure getting the first 6 levels of Paladin at least before dipping in Warlock. Get to 8 first if going for the 17/3 mix. I'm also open to other suggestions – I considered Oath of the Crown solely for Spirit Guardians, and I think it could fit with a Helm or Tyr-worshipping Paladin, but it's iffy for a half-elf. I could also be persuaded about different Warlock Pacts.
TL; DR
Is a 3rd ASI or the Resilient/War Caster feat worth losing Holy Weapon, Banishing Smite, and Hold Monster. Do the OAs granted by War Caster (for use with Booming Blade or Green Flame Blade) outweigh the more general benefits of Resilient (CON).
(A question flagged as a possible duplicate concerns a different Patron and Pact than is discussed here.)
Best Answer
Paladin 16 / Warlock 4 is the strongest option from the list
As you have only one 5th level slot on level 17, you do not lose Banishing Smite and Hold Monster, only one of them per day. By this level Resilient (Con) provides +6 on Con saves, all the time.
5th level Paladin spells are weak
Banishing Smite is only really useful if the enemy gets below 50 hit points, and on level 17 it is quite trivial to kill something that has only that many HP.
Hold Monster can only be cast on one target with your slots, and on level 17 most worthy targets have either really high save values, Magic Resistance, Legendary Saves, or a combination of these. If you could upcast it to target more creatures, the chance of wasting a turn and your highest level slot were reduced, but you can't.
Holy Weapon is better than the above two combined, but it still comes into play too late to matter much.
Think of them this way: A 10th level Bard (with Magical Secrects) can cast any spells you could on 17th level. It is not owerpowered for him, so it must be weak for you.
Paladin 12 / Warlock 8 is better
+5d8 twice per short rest is stronger in my opinion than anything you could get from Paladin after level 12.
You got Improved Divine Smite and ASI, great place to leave.
What you lose
Soul of Vengeance is good, but you can get the same effect out of Sentinel with some smart maneuvering.
Aura of Courage with 30 feet radius is great, but only marginally better than with 10.
Party members who perfer to be in melee can remain close to you, and the others should be more than 30 apart if possible, as it is the walking distance of most monsters.
What you gain
The two 4th level slot per short rest is already mentioned.
Spells: Counterspell1, Dispel Magic, Fear, Fly are all quite good on a frontliner, and Greater Invisibility is especially great for DPR.
Invocations: Another two over what you could have with 16/4.
1) You have to be in 60 feet of the casting enemy, so you are in better position mostly than your caster colleagues