It depends how good you think he is...

If he really is as great as he thinks he is (don't forget he called Winky out) and Wright beats Hopkins then that is definitely the biggest/hardest fight for him as far as legacy goes.

As it stands at the moment the hardest test with most marketability would be Mosley. They are both WBC Welterweight Champs and Shane has two wins over Oscar at 147 & 154, easy sell.

The next biggest fight right now would be Hatton, he has a massive fan base and being the lineal champion at 140 and an undefeated 2 division champion a win over him would look great on your resume, especially when he took the belt from Kostya Tszyu!

If Cotto destroys Judah then you could put his name up along side Mosley's if he wins a close decision then I'd place him with Hatton.

There really is no other names big enough out there. oh... wait... hold the phone!!

If Spinks upsets Taylor then you have the perfect opponent, former Undisputed Welterweight Champion and current Undisputed Middleweight Champion. He would by no means be the hardest opponent but he would hold the WBC Middleweight Belt.