Tierlist, you say? I'd say the main characters might have to be tiered separately from the Rebellion cast in that case. So far, I've got a good idea on how good or bad some of the rebellion cast are:
(based on Pokemon tiers)
OU:
Abadede (good priority and range, massive damage, solid moveset, combo potential, super armor)
Break (pretty much Axel minus a few things, plus a speed-up gimmick that makes up for the missing handful of moves. Blazing fast, good combos, and pretty resilient)
Monalisa (good number of strong ground projectiles, basic kick attack that can stunlock small groups of foes, good jumping attacks)
Bruce (long-range basic attack that is fast, moderately strong, and can perform long-range combos, knockdown specials good for launchers into juggling)
Yamato (long-range expert with some pretty cool move tricks)
Shiva-3 (Great range, damage, and speed, brutal Rage move)
Raven (nice combos and damage, has a brutal stun-lock grapple combo, good block game)
Robo-X (ranged combat expertise, powerful charge and Rage moves)
Tracker (can gain plenty of speed with slide kick, good ranged moves and combo, decent pummel)
BL:
Roo (Good combo abilities and a nasty back throw)
Shiva-2 (rage isn't as powerful as 3's, otherwise similar)
Rocky Bear (good juggles, decent jump attack, powerful basic attacks)
Zamza (awesome comboing and high speed, plus blocking, but so-so damage on moves like Rage)
Kusanagi (good variety of moves including air projectiles and dodging, kick makes a good low poke, good weapon usage)
Jet-3 (can set up bomb traps, good combo and grappling game, is levitating)
Mr. X (good ranged attacks, powerful gun swipe, but poor speed and lacks Rage)
MacLeod (easily repeatable ranged attack, easy to grapple with)
UU:
Garnet (poor start-up on basic attack, but her other attacks are pretty solid, decent air game)
Jet-2 (same as Jet-3 but with less moves)
Big Ben-2 (fire breath does nice damage, good stun on slaps, decent air game, but sluggish)
Electra-2 (She's... okay i guess? I like most of her moves, but they seem to have fairly poor timing, even if accurate to her enemy self.)
Harakiri (sluggish and can't jump, but good damage and range)
P-1 (Is able to leap around the screen with ease and has good damage on its moves)
RU:
Electra-3 (Pretty much Electra-2 minus jump attack)
Big Ben-3 (The rolling attack is a poor move to use due to the dizzy time)
Donovan (Good enough combos but weak damage)
Hakuyo (attacks give good amounts of stun but do poor damage, and his special has a lot of startup)
Galsia (Surprised? He has enough variety to keep him out of the doldrums of NU, and when he gets a knife... watch out.)
NU:
Slum (Not very good with his attacks)
Vice (Basically an even worse Slum, he’s very weak all around)
Signal (despite his throw and slide, his normal attack is awkward to use)
This tierlist is relative to how well they can complete the levels of Normal, mostly for SOR2 route. Rage, counter, and juggle are taken into account. It's not really intended as criticism, just a guideline for players.