both are good jujitsu guys from Brazil but Machida has better jujitsu and even better stand up! Sure he backs up but he's more of a counter striker like most martial "artists" He's already beaten BJ Penn, Rich Franklin,and Tito Ortiz. He also grew up training with Anderson Silva (can I see a vid of them sparring!!) Imo with his size he could possibly challenge 4 out of the 5 belts if he wanted to.
I don't think Thialgo has fought near the amount of talent Machida has. Drwal had him beat until he gas'd