Sonic would definitely do those spins around Zero, leaving Zero pretty much helpless in reacting to whatever attacks Sonic has in mind for him. Sonic is quick, agile; Zero's slower, but packs more punch. Sonic's just made of flesh, bones, and those ridiculous-looking sneakers; Zero's a badass android with a laser saber pretty much reminiscent of Star Wars Jedi light sabers.

Sonic could pull off those mean tricks at Zero, but he wouldn't be affected easily; he is, after all, an ANDROID. Zero, on the other hand, is slower than Sonic but once he could just get a hold on the blue speed freak, he'll take off a hefty amount of rings or fruits or whatever Sonic uses for his life meter bar, and the hedgehog could just keep on streaking. Eventually, once Sonic gets drained by many of Zero's inconsitent yet very powerful attacks, he'll slow down (assuming that we are in the real world of Zelaron Melee) and eventually Zero would catch up to him and turn him to hedgehog fritters. BTW these are taken into account when Zero gets up close and personal with Sonic in one of those rare times Zero does catch him.

Now, if assuming that these 2 combatants are in a locked room, Sonic would have less room to zoom around in, unless the room comes equipped with those loops so he could catch more rings. But since the room is just closed and tightly packed, Sonic would find it very hard to keep himself at mach 1 or else he'll just crash himself into a wall. If the room is HUGE then Sonic is just WAY too much for Zero to handle as Zero couldn't possibly dash all around the room to silence a hedgehog with a serious need of a haircut.

As with most video games, knowing the terrain and playing to one's strengths is the key to success; so if Sonic has as much space to sing "The Sound of Music" with a zillion football fields to spare, then Zero's completely !@*#&*#(@ up. Then it's the other way around if the room they were fighting in is in an enclosed space (unless Sonic could also climb walls by means of his mach 1 feet aerobics; but then Zero would toast him via his Rakuhouha special).

So I think, given these considerations...anybody would be victorious.

But I'm putting my hopes on Zero.

Life is short.
Let's all grab a BEER~~~!!!