At 3 times HW champ over a long time span surely Randy has to be number 1 as the most successful HW of all time. Coming out of retirement to beat Sylvia, being a relatively small HW and fighting much bigger guys sets him apart.
Comparing skill level with todays fighters is pretty much impossible with the evolution of skills, but I dont think Randy has a peer on that list to his achievements. The only one who has a hope to do it is Cain.
Eh.....yeah he was a three time HW champion but I would rank him higher at LHW and p4p than at HW.
Big HW Wins
and the the HW loses
He was basically a .500 "champion" at HW but at LHW he lost to Machida, Liddell, and Belfort that's a hell of a lot more impressive in my eyes.
For me I have Fedor at #1 just because of who he defeated. Antônio Rodrigo Nogueira and Mark Coleman likely "acheived" more winning titles in both company's