I'm going to refer back quite a bit to what was said in the "What are the strengths and weaknesses of each follower?" question in this answer.
- The Templar is ideal for those who need a tank or require healing
- The Enchantress is ideal for those wanting crowd control and decent
damage
- The Scoundrel is ideal for those wanting pure damage and a little CC
ability
So taking that the Scoundrel is your best chance for direct damage, your first step is to gear him properly with as much Dexterity increasing gear as you can to maximize the 2.5x multiplier.
For his skills:
Level 10 - Poison Bolts
Level 15 - Personal Preference
Level 20 - Multishot is better for AoE mobs, Powered shot better for
boss fights
Level 25 - This will depend on your current class and its focus on
critical hits. Hysteria if you do have a high crit rate, Anatomy if
you don't.
Direct DPS from your follower is not always the best strategy to follow, you might want to consider some alternatives of how you use your follower.
Alternative Follower DPS Boosting Strategies
A good alternate path to follow is to pick the follower that can give YOU the most benefit and increase YOUR DPS. In that case, I like the Templar with his level 20 Inspire ability, particular as a melee class. It allows me to bring a more consistent stream of Spirit or Fury spending tasks, and since I can provide MUCH more DPS than a follower, i think that is the best course of action.
Another benefit you get with the Templar is that since he is a tank, and will charge headlong into combat, you can give him lots of indirect DPS through items that contain "Thorns" damage. Some rings, amulets, and shield will possess this damage, and at high levels they can possess enough to likely outpace the follower weapon damage output. If you decide to gear your Templar this way, be sure to give him items with the highest armor and strength/vitality possible so he can survive the pounding.
Life: Yes, yes it does. This is easy to test, just toss an Amethyst into a socketed helm with no Vitality on it. Since there are no other stats or affixes on items that affect HP beyond those two, there's no need to go into more detail on the formulae here I hope.
Damage: See here for all the details, but in short: Yes, it accounts for everything that matters. The only damage boosting stats it does not take into account are bonuses to the damage of an individual skill, or increases to resource capacity or regeneration.
Protection: It includes Armor, Dodge, and Resistance, but this is new. As of patch 1.03, "Resist values will now be taken into effect when calculating the Protection comparison stat (the Protection value is an average protection estimate of all your resists)".
Best Answer
As far as I know from personal experience playing the game, cooldown reduction can spawn in seven different slots (max value for level 70 rare items given in brackets):
There are no legendary items I know of which would give an extraordinary reduction to all skills (however, there are certain legendaries which specialize on cooldown reduction of single skills). But generally:
Where X% is either 9% in case of weapon, or 7% for the other mentioned slots.
Apart from items, there are diamond gems, which reduce cooldown when put into a socket in a helmet. The highest tier gives:
Every character can get cooldown reduction from Paragon Levels through Paragon Points:
Finally, the best character class for the cooldown reduction stat is Wizard, since this class has a passive skill giving:
Now, we should keep in mind that even though the symbol % is used to quantify cooldown reduction, the formula which combines the different amounts from different sources is not additive but multiplicative. Therefore, for all the above contributions we get in total (assuming all legendary items):
1 - 0.8*0.9*0.875*(0.92^6)*0.9 = 0.656...
So that, apparently, the maximal achievable effective cooldown reduction is 65.6% (generally, not talking about specific skills for which specific legendaries provide a much greater reduction). I heared that much higher values of over 74% could be achieved during the beta. However, Blizzard nerfed many things for the release, so that this might just be one of those. If I missed something, let me know.