Done a quick breakdown of the TUF 17 cast, and ranked them (my personal opinion after quickly researching them).
As for the beast of the show, like others my guess is Tor Troeng. Part time rapper Kevin Casey is also a nasty dude (http://www.youtube.com/watch?v=Nc2N2TiKI3o
), Nik Fekete is a Division 1 All-American wrestler, Jimmy Quinlan is a BJJ world champion, Adam Cella a star kickboxing golden gloves champion with over 60 fights, Uriah Hall is a beastly athletic muay thai fighter.
My guess was that it has to be one of them 6. Gotta be Troeng, if not my next best guess would be Cella or Hall.