If we are not counting abilities then I would say L.

If we're going to make master plan to find out who the imposter is then light, lulouch and ayanokoji are the best candidates.

If we're looking at the best abilities then Aizen would murder everyone here.

And i guess that godsuya is kind of a cheat character. He can just "scan" the whole map to see what's happening and can use the eidos system to "restore" the characters.

Lelouch and Light would win as impostors, but maybe not as a crewmates (because of their solo play style). Ayanokoji, Erwin Light and Norman look like they'll win as crewmates (because of their ability of deduction and skill of using others).

I don't know about Tatsuya since he mostly shines in his anime because of his physical abilities.

And I haven't watched Bleach so IDK about Aizen.