Chaos doesn't sound too special to me. I don't think creating time loops will help against defeating Sin.

I have to say that the Emporer might be able to beat Sin, since he became the King of Heaven and Hell. That's quite a feat there.

Don't know much about Cloud of Darkness...

Many people are saying Zeromus can beat Sin, but I don't think this can be considered correct. In his first form, Zeromus may be invulnerable to physical and magical attacks, but he can't fight until he is hit. It was only in his second form when he started to relentlessly attack. I think this was why in his first form, Zeromus was only able to attack the party when Golbez and FuSoYa casted Meteor. And I think this is also why he would sit there doing nothing until Cecil used the Crystal. So all Sin would have to do is...nothing! And the battle would be a stalemate.

Neo X-Death could most likely beat Sin. The Void is the most powerful force in FFV, with the exception of the Crystals.

Kefka could beat Sin as well, since he had the power of the Statues, and the game said that the statues had control over all magic in FFVI.

I think Sephiroth might have a chance against Sin. In FFVII, even though he didn't control all of Lifestream, I would probably say he controlled a good amount of Lifestream (most likely half). The rest of it was controlled by Aeris and the planet. And half of the planet's energy might actually be enough to beat Sin. Not to mention he was also powerful enough to contain Holy's power, one of FFVII's most powerful forces.

Sin would kill Ultimecia long before she could achieve Time Compression.

I doubt Sin could blow up Spira in one attack, even with Giga Graviton. But Trance Kuja could, so Kuja wins.

As for Shuyin, he himself cannot possibly beat Sin. However, he probably could with Vegnagun.