Its pretty much either Nelson or Muurr at this point. I think SF is probably deeper in terms of their top 5 with Fedor, Reem, Werdum, Silva, Arlovski. The only thing is, after them, there's Cormier who has tons of talent but is unproven, Rogers who's pretty much considered a bum at this point, and Lashley who has looked impressive, but who knows how good he is, his 5 wins are all over cans. The UFC has way more depth after their top 5 with proven fighters like Nelson/Muurrr, Nog, Herring, Rothwell, Yvel, Cro Cop, Duffee, Russow, Gonzaga, etc. None of them are really world beaters, and some of them have names bigger than their actual performance value at this point in their careers, but the depth is there. The top 4 are just at a higher level at this point than the rest of the division.