Sharla - I primarily play as Sharla for several reasons. First, her long range weapon makes it the most convenient to take out lower level enemies with. Secondly, you don't have to be concerned with your position in relation to the enemy during combat. In addition, since she doesn't have to be up close to the enemy, then it is easier to tell where she is on the battle field even when things can get chaotic at times. I usually feel more in control of determing the party's fate because of Sharla's healer role. Also, she has nice boobies.
Melia - I started to play as Melia once she joined the party. I heard that the she is more powerful when the player controls her as opposed to the AI and it's always refreshing to play as a different character anyway. With that said, I'm not a fan of her cliche character design and don't particularly like the how it takes her a few seconds to set up an attack, but it is nice to be able to cause topple on your own. However, I have to admit that her
is the coolest attack I have seen so far.
Dunban - He's the badass of the group and one of the most likeable too. I would like to control him more often because his moves are fun to perform, particularly the kick-related attacks. However, I feel compelled to make the most effective team and since the AI handles him well, I simply stick to playing as someone else. As far as close-range uses go, Dunban is by far my favorite.
Shulk - His Monado moves are pretty cool but his regular move list doesn't seem to evolve much. I'm not a fan of his character design and trying to take advantage of his back and side melee attacks on enemies can be time-consuming if aggro is focused on him. I will say that he does have some amusing battle victory one-liners.
Reyne - Unfortunately, I don't have much use for him. He's a good tank character but I don't see a need to use him when Dunban can do what he does by dodging attacks instead of taking the beating. Also, Reyne's move list is probably the most boring out of all of the characters.
Rikki - He's a funny support character with an oddball move list. Unfortunately, I can't find a place for him on the team as there's already a good tank, healer, and damage dealer. The only time I control him is when wanting to travel long distances faster while ignoring combat. So I just equip him with quick step gems.