Since I'm bored I'll just put this out there: I don't think a categorical SP/Coop tier list would be possible at all because it depends way too many factors, the main ones being level design and what you're trying to accomplish in the level in question (for instance, are you trying to beat the level as fast as possible, get all the emblems, get all the record attack emblems, or just have an easy time?).
For VANILLA SRB2, in terms of just beating the game as fast as possible, Sonic is obviously the best because the levels are quite horizontal most of the time and he's stupidly fast. But if you're ranking them by anything other than speed, however, Tails generally wins. Knuckles is pretty much middling no matter what unless the level design either has way too many climbable walls or way too few climbable walls, both to an unacceptable extent...
Vanilla SRB2 very much lacks mostly vertical levels, but in those, Tails generally wins too...but again, there's always variables, like just how vertical the level is, what Knuckles can climb on, if Sonic can monitor bounce to cheese it, etc...