For those who play Diablo 3, they know that there are three followers available in the game. They are the Templar, Scoundrel, and Enchantress. Each has unique strengths and abilities that can prove to be useful for your character, and they fight at different ranges with varying degrees of effectiveness in different situations. Knowing which to use for your character can mean a difference between a hard time and a good time.
While followers aren't exactly good in terms of DPS, their abilities can prove to be very useful when you're playing solo. Each one can work well with different character classes, so it's worth noting which one can work best for your character. Picking the "wrong" one can prove to be a hindrance to your journeys, but at least you can change it later on and test the others out for yourself. Here's a list of recommended followers for each class to make things easier.
There is no question that the Enchantress is the best choice here for augmenting the Barbarian's strength by providing crowd control and stun against enemies. The Scoundrel is also a good secondary choice for those who want to change things up every once in a while.
Since this is a ranged class, you would want the Templar to go up front and tank damage while providing healing and defensive bonuses to boost survivability in the game. The Enchantress is also effective as she can provide extra ranged DPS and provide crowd control with her abilities.
The Monk is a bit more versatile as a character class, so there really isn't a "best" follower to back things up. The Enchantress can be a pretty good choice due to the crowd control; the Templar can provide tanking and hit with some effects; the Scoundrel can provide ranged DPS and damage buffs.
Certainly, the Templar is the clear choice for the Wizard, whether you're playing a melee or ranged Wizard. The Templar can tank damage that definitely should not be received by your Wizard, and the taunt abilities can draw fire away from you. The Enchantress can also do well with the Wizard as she effectively doubles magic effects and add in to ranged DPS.
Much like with the Wizard, the Witch Doctor can benefit from the Templar due to the same reasons. The Enchantress can also be a good secondary due to crowd control and additional magical DPS. You may find that the Witch Doctor's various skills can sync up well with either the Templar or Enchantress, depending on your build.