1. Fedor- his resume speaks for itself. Never been defeated (i won't even begin to discuss the loss on his record because if you consider that a loss, you're a moron). Has dominated every opponent he's ever faced, not to mention guys much bigger than him. Has defeated the 2nd greatest heavyweight of all-time twice (Big Nog)
2. BJ Penn- hasn't lost a lightweight fight in 8 years, and that was a decision when he was 22...this was so long ago that he actually had hair. This guy has only lost to the best of the best, and those guys were much bigger than him and at higher weight classes. His first fight against GSP, he was robbed despite leaving GSP a bloody mess, and the 2nd time, he cheated. He submitted Matt Hughes, the greatest welterweight of all time, in the prime of his career in the 1st round, and in the rematch he was destroying hughes until breaking his rib. He cleaned out the lightweight division in 5 seconds without even trying.
3. Anderson Silva- never lost a UFC fight, ran through the UFC weight division in 5 seconds, destroying the overrated UFC poster boys Rich Franklin and Forrest Griffin and showing them that they are indeed inferior athletes.
4. GSP- as much as I hate to admit it, GSP, despite being a gay rights activist, is a great wrestler. Ever since his embarrassing performance against Matt Serra, he has lay n prayed plenty of opponents on his way to victory, and at this moment seems to be as unbeatable as any UFC champion.
5. Shogun- after dominating Machida all 5 rounds, the judges decided to rob Shogun because he fought for Pride and it would make Dana look bad if all the Pride guys came over and took all the belts (which they already have anyways.) With wins over Machida, Liddell, and Rampage, Shogun will be the greatest LHW of all time within a year or so...
6. Hendo,Mousasi, Brock, Rampage, and Aldo- all are honorable mentions for their current status in MMA, but are currently not the top dogs in their weight class (except Aldo, who has only recently become champ)