Diablo 3 Followers
The three followers in Diablo 3 are the Templar, Enchantress, and Scoundrel. They each play a different role in how they assist you but they are primarily there to assist and boost your own power. You get access to the Templar and Scoundrel in Act 1 and the Enchantress in Act 2. Once you get them you can equip them with a compatible weapon, neck, and rings. They won't in their own right produce much damage due to the restrictions Blizzard put on their damage, but their abilities and equipment can prove very beneficial to your hero in the quest to 60 and farming beyond that point. Let's go into detail about each one of them.
The Templar is the first follower you get early on into Act 1. He is primarily focused on being a melee fighter and tank. He possesses healing abilities, damage abilities, taunts, life restoration aura, and passive resource regeneration. The resource regeneration isn't too impressive, but for a fury barbarian or monk it would be useful. The healing and taunts are very helpful when leveling because it keeps you alive and allows you to fight longer and harder. I would say that the Templar ranks as the best level up follower due to the melee tanking and taunts as well as the constant healing. Once hitting level 60 however, he quickly falls behind the Scoundrel and Enchantress because the healing is now minimal and the taunts aren't really necessary. The resource regeneration passive would be the only reason to use him post 60.
When equipping the Templar, make sure that you give him a lot of vitality and armor so he can taunt enemies off you and take a beating. He won't be doing damage so use him in a more tank oriented way to help you in your adventures. Once you hit level 60 and start farming, it would be useful to load the Templar up with a lot of Magic Find gear so it can give you a bigger MF% number which will assist in finding more magic items.
The Scoundrel is the second follower you will acquire while progressing in Diablo 3. He is gotten shortly after the Templar joins you. The scoundrel is a ranged fighter using bows and arrows instead of getting into melee combat. He has a lot more crowd control in his arsenal and abilities unlike the Templar, but will die very fast in melee range so he isn't as useful when starting to level. Depending on how you build him you can go more a damage ability route or a more crowd control ability route. This follower is best used as a crowd control bot since he can blind, slow, and stun. Again the followers have low damage so until you get some amazing level 60 gear he won't be doing any damage so this is his best role. His two final abilities are great passives, it's up to you which you find more useful. 10% more damage for 3 seconds after a critical hit (cooldown of 5 seconds) or a passive 3% crit for both you and the scoundrel. I prefer the passive crit chance, but the extra damage can be useful as well. The Scoundrel really shines at level 60 when you can give him some of the gear I list below. I prefer the Scoundrel of the 3 followers at level 60.
When gearing the Scoundrel, he is best served with having high attack speed rings and a neck so he can attack more. For his weapon, I like to continue the crowd control this follower offers by getting a Windforce with high knockback or a good freeze % piercing Buriza-Do Kyanon. These two weapons combined with the Scoundrel's multishot ability will be continually freezing and knocking back enemies and with high attack speed the crowd control is excellent and will really help you.
The Enchantress is the last follower you acquire in your travels. She will be gotten in the beginning of Act 2. The enchantress is a magic caster so she is ranged just like the Scoundrel. She uses staves and 2H swords. The enchantress is also very prominent with crowd control abilities but also has abilities to buff your hero as well. From disorients and charms on enemies, to armor and attack speed buffs on your hero, she is very versatile and helpful but she is extremely squishy and will die very fast if caught in combat. All throughout the game and even at level 60 she is useful for her crowd control and buffs, but at level 60 I find the Scoundrel's weapon choice more effective and practical while still dealing some damage. She is great for those who need the attack speed boost and want some more protection, so she is a great choice for melee characters as well as ranged.
When gearing the Enchantress, her primary role will be to add a significant amount of Magic Find to you so load her up with MF% gear. Her auto attacks don't benefit from any nice crowd control effects like the Scoundrel so don't bother focusing on damage and attack speed. Instead use her as an MF% bot and let her buffs and crowd control do the talking.
So who's the best?
In the end each follower has a bunch of pros and cons and they don't offer a lot that makes or breaks a hero's journey at level 60. They each assist you with defense and offense, but don't really bring much damage to the table. In my opinion the Scoundrel offers the most bang for your buck with all the crowd control he brings to the table, but the enchantress can really be a great help against tough elite packs by charming, hexing, and disorienting them. The Templar if geared well can really tank and take a beating so he can keep the elites and tough enemies off your hero if he/she is squishy. It's all personal choice, but you really can't go wrong in your decision