To me "Sonic" is the gameplay style of the first 3(?) games. I played the isometric game for a bit ages ago, but that wasn't "Sonic". Dunno and don't care the least about the later games/shows (I think I had one listen to the voice they game Sonic in one game and turned it off)/comics, etc.
To me also "Mario" was always the gameplay of the first few games also (as well as the numerous reboots/style copies/whatever they have on modern handhelds and such). I did play Mario 64 ages ago as well, and that was okay, I guess. I wasn't particularly moved to finish it. Dunno and don't care the least about the later games/shows/comics/etc.

In that very limited frame of reference, I definitely still prefer Sonic to Mario. Mario games just seemed slow and boring. Could just be the nostalgia talking, of course :D.