Despite the fact Khabib is the only fighter on this list that retired undefeated, I still think his resume is lacking and in my opinion, he never really carried that same aura that Fedor, Silva and GSP had. You can pretty much ignore his early fights in Russia, as his record during that time is littered with unknowns. In his 8 years in the UFC, he went 13-0 with 7 finishes and 6 decisions. It's a good record, but not exactly seemingly invincible.
GSP fought the best of his division for years, and even though everyone pretty much knew what style and gameplan GSP was going to bring to the table, still no one could really stop him. He outwrestled the wrestlers and manhandled the grapplers. Honestly, the Nick Diaz fight was probably his most surprising fight, given that most people expected him to take Diaz down, beat him up, rinse and repeat. He outstruck Diaz, and that does speak volumes towards GSP being a well-rounded fighter. When he was the challenger, he was a finishing machine. As a champ, he fought safe, and even though I knew he was capable of finishing many of his title defenses, it was his record and the amount of zeroes on his paycheques that made him play it safe. To be fair, I can't really blame him, and I am not sure I would have done it any differently if I were in his shoes.
Jones simply has too many asterisks (again, in my opinion) working against him. While he enjoyed many physical advantages (size, reach, youth) over most of his opponents, he still felt the need to cheat and fight with questionable tactics (eye-pokes, oblique kicks). There is one reason and one reason alone why you would literally hide from USADA officials, and it's not because he failed to wear clean underwear that day. The other argument being his record padded with aging and blown up MW's.
Silva had one of the most emphatic UFC debuts ever against Leben, and was a sign of things to come. I can't recall another title fight where the champion was thrashed so soundly as Rich Franklin was. It was as if Silva was fighting a complete amateur. Silva was a highlight reel one-man wrecking crew during his title reign, and it would be pretty hard to argue against him and him seeming like he truly was invincible during his prime. Even when he was being controlled and dominated by Chael, he still found a way to remain composed and still end the fight with a highlight reel finish.