Tiers in my opinion:
Wolverine, Sentinel, Omega Red, Colossus
Psylocke, Cyclops, Iceman
Wolverine - Not many weaknesses, except maybe getting zoned or out-thrown. His super is probably the best guard cancel super in the game. Once he has full meter you must be very careful what you do when he’s on the ground.
Sentinel - Gives the most damage and takes the least (except for throws, since heavier chars take more). Has the shortest OTG time (eg, he wakeup rolls faster than anyone). Only real weakness would have to be size, penalty if you DON’T roll and blockstun while flying issue (don’t get caught flying low to the ground).
Omega Red - Coil combos do big damage + give him back some life, and counter throwers can’t tech hit them.
Colossus - Gives big damage and doesn’t take as much. His super is also very good when used as a guard cancel, but you have to be more careful and make sure it actually hits. The long ass recovery on it isn’t good vs characters who wakeup roll fast. While shoulder charge armor + super armor helps, he’s screwed against someone good at zoning.
Psylocke - Speed demon + huge combo potential. Super has no recovery even if blocked. Downsides are: weak vitality, long OTG time, REALLY long wakeup into dizzy time, have to be careful with psi-blade since it’s recovery is long.
Cyclops - Decent damage, good normals (in the air especially), good combos, good throws (beam throw especially). Downsides: Optic blast sucks, long OTG time and long wakeup into dizzy time.
Iceman - MP throw -> super, beam resistance, nice normals. Specials aren’t all that good.
Storm - Another speed demon, dash has invincibility frames, run away, typhoon speed. Downsides: really crappy vitality, deceptively bad range on her normals.
Spiral - Unblockable traps, super is also good as a guard cancel. Teleports are useful but are very vulnerable. Downsides: really crappy vitality, her teleport tech hit is vulnerable on re-appearance (but you can vary where she appears to lessen this weakness),.
Silver Samurai - Does decent damage and good for chip, but tons of downsides. If you’re hit out of supers on startup, you lose some meter even before they come out. Size and weight make him a combo dummy, slow overall, and combo potential isn’t nearly as good as all the other characters.
I’d say the split between tiers isn’t that big except for Silver Sam. He has an uphill battle.
Kind of hard to place Akuma, I have problems with the code myself, and I haven’t seen many use him effectively.
Edit: What board do you have? There’s some character differences between Japan/2.X boards and US/Euro/3.0 boards.