TIER 1
Eren: Eren's special is pretty much pure death. You kill big Titan's in three punches and little ones with one kick. Although he's a bit slow and basic, once that special is up good bye Titan's.
Jean: He's fast, simple, and his special is a get out of jail free card. Even though I hated him in the anime I'm gonna have to give him tier one.
TIER 2
Captain Levi: Levi's special is very efficient and easy to hit, and his speed is unmatched (other then Potato Mode Sasha). Levi is just solid all around.
Mikasa: Mikasa is a very good character for beginners and experts alike. She's just all around good, lacking on mobility but that doesn't matter as much. Plus it's Mikasa... so... yeah.
Marco: Marco is a solid choice if you have been playing the game for a while. His special, which attracts Titans to you, is an easy way to draw the Titan to an easy killing place while keeping a safe distance from other Titans.
TIER 3
Petra: Her special is just so cool, and can be used as a sick looking dodge if timed right. The only problem I have with her is her speed. If you're using your hooks right then you won't have a problem, but her dodge/walking speed is sooooooo slow. Also her special does a number on your blades. Overall she's not bad, but not great either.
Sasha: Sasha is very basic. The only way you will be killing Titan's is your basic attack. Her special spices her up a bit though. The speed boost is nice for closing in/ dodging a small Titan, and running away from the crawlers.
Armin: Armin has one of the better specials in the game... if it goes off. If it doesn't you better be ready to dodge. If it does, well you just bagged yourself a free Titan kill m'friend.