The Sonic games haven't been remade, they've just been re-released. There's a difference. And if you're on about SA1 and SA2, they're basically just the original games but with added features to work with the Gamecube.
I'd have to say one of the best remakes I've played is FFIV for the DS. Even though I never played the original.
Worst remake... Probably Tomb Raider Anniversary. I loved it at first, but now I look at it, they pretty much raped Tomb Raider 1 to bits.