Board Thread:Speculation, Theories, and Rumors/@comment-25912037-20141223043619/@comment-26137541-20150608231527

What context are we speaking in? In the games, it's a deadlock between Sonic himself, Knuckles, Shadow, Blaze, and Silver. The latter four matched or defeated Sonic before, and they all have Super forms. Perfect Dark Gaia might also be thrown in the mix as he was an equal to Super Sonic or possibly stronger. Although their canonocity is debatable, Sonic and Knuckles have Hyper forms, putting them above the other three recurring characters. Solaris could also be a contender, with his temporal omnipresence, devouring time itself and requiring three Super characters to defeat, although he is almost assuredly non-canon.

Of course, if we talk about Archie, anything from the games is rubbish in that verse power-wise. If you want the strongest character in that canon (and probably all of Sonic), it's probably the guy in your icon, being the most proficient user of the Chaos Force to date.