There are a lot of people underestimating Thiago. I think without the Serra defeat then you would have to probably say GSP is the best. But it did happen. And if I'm looking at dangerous opponents I would rank Thiago waaaay higher then Serra. Plus its gonna be a lot harder to push a big guy around.
So we shall see...
Thiago is obviously the most dangerous person to GSP's title to date. This being said Thiago has never fought someone as great as GSP, much less beaten someone on GSP's stature. If Alves wins this fight it would be a major win for him, a lifechanging win and a big upset imo.