Since I am an MMA elitist, I will settle the record on GOAT in MMA. There are only two currently, Fedor and Silva. Fedor fought the very best in the HW division and destroyed all of them for about 5 years. There was no one in the UFC at that time that could touch Fedor, the best HW's were in pride. MMA began to evolve around Pride folded and Fedor couldn't fight some of the best arriving in the UFC. Because of Fedor's dominance for so long in a division that can't keep a champion, he is one of the greatest ever.
Anderson Silva doesn't need an explanation, we have seen everything he has done for the last 6 years and he has destroyed all of his fighters (except for one).
GSP is a close third, but he will probably get humbled by Silva if the fight happens.
I am not sold on Aldo lately just because he hasn't looked as dominant in the majority of his UFC fights, and I think Frankie has a good chance of winning.
I think I read somewhere that he has had some cutting issues. At the start of his MMA days he'd sometimes need his gym to feed him b/c he wont have eaten. Now he's well better fed he's actually a big guy. His easiest cut it was commented was against Chad Mendes where he looked his dominant self again. Think he destroys Frankie.