The debate about who are the best pound for pound fighters in MMA has raged on for years, with very few people coming to coming to a consensus. First off, pound for pound is defined as a term used to describe a fighters value compared to fighters of other divisions.
So let's start at #5
I personally guarantee that this man is going to be the #1 within the next five years. At 23 years old, he has already stacked up a record of 25-2 with one draw. That includes wins over Melvin Manhoef, Denis Kang, Hector Lombard, and Ronaldo Souza. Twenty-one of his 25 wins have come in the first round. He's been finishing off his opponents almost equally with 14 KO's and 8 subs. Only 3 of his 25 fights have ever went to a decision. Furthermore, Mousasi recenty won the 2008 DREAM Middleweight Championships. He is a young well-rounded, intelligent fighter who is full of promise, which is why I give him my #5 spot on the list. You can look for him to solidify his P4P status as he takes on Renato Sobral at Affliction Trilogy and Sokoudjouat DREAM 10.
Migeul Torres has one of the most unblemished records in MMA. Greater even then that of Fedor. At 37-1, Torres is currently on a 17 fight win streak spanning over almost 6 years. The fact that he fights at Bantamweight a weightclass that isn't used in the UFC results in Torres not getting as much credit for the casual MMA fan, which is unfortunate because Torres has put on some of the most exciting fights in MMA history. The battle he had with Yoshiro Maeda was probably the fight of '08, and in his demolishing of Tapia he showed his diversity by throwing in moves, spinning back fists, cartwheel kicks, that are rarely used in MMA. He utter dominance in his division and in his career in general earns him the #4 spot.
This is going to piss a lot of people off so I'll do my best to explain myself. First, Silva gets only the #3 simply because I'm looking at a career in whole. My criteria involves record, names, and most importantly, how they have performed lately. Silva is 24-4, a very good record, with 14 of those wins coming by knockout. He's defeated easily some of the best names in MMA; Dan Henderson, Rich Franklin and Hayato Sakurai, and a lot of other tough competitors like Lutter, Cote and Irvin. But lately Silva has not been fighting like a P4P champion so I see no reason to give him either top 2 spot. His fight against Cote was a joke, and although his fight against Thales wasn't entirely his fault, with Thales flopping around like a dying whale, Silva still did not put on the performance that he should have. Nonetheless, he is easily one of the best fighters to ever fight in MMA and he gets the #3 spot.
Georges St Pierre
Georges St Pierre is a machine. If it weren't for the Serra speedbump I might have given him the #1 spot. He's got 2 loses, one against Hughes when he was in his prime and GSP was a barely more then a rookie, and his unfortunate loss to Serra. He's got a record of 18-2 with wins over fighters like Karo Parysian, Mayhem Miller, Sean Sherk, BJ Penn twice, Matt Hughes twice, Josh Koshcheck, and Jon Fitch. He has dominated his last 5 opponents with a mixture of wrestling, ground'n'pound and solid striking. He has pushed Fitch to the end, beaten one of the greatest ever fighters, Matt Hughes, twic. He's well-rounded, winning 8 of his fights by knockout and 5 of them by sub, and most importantly he's still in his prime. At 28 years old, he's got a long, bright career ahead of him. Hopefully he'll keep it up when he takes on Thiago Alves this summer.
Obviously. There is very few people who don't see him as the #1. Unfortunately one is Dana White, which means it might be a while before we see him fighting in the UFC. But Fedor is 30-1. His only loss should be a no-contest. He has dominated every fighter. It has been argued that he has never lost a round ( Arona, I believe, took rounds off him ). He has beaten every single big name thrown at him. Arlovski, Silva, Arona, Cro Cop, Big Nog (2), Heath Herring, Sobral, and Matt Lindland. He's won 16 of his fights by sub. and 7 by KO. He has never been submitted or knocked out. Neither of his last two fights, both against former UFC HW champions have made it out of the 1st round, and he doesn't seem to be slowing down. Some claim he is a cyborg. I wouldn't be surprised. He takes the #1 spot easily.