Pound for pound debates are pointless fun. Here goes!
Rankings are a mixture of past performance and anticipated future results. I think, in order to be eligible for #1 P4P, you have to have at least one title defence.
I believe when making these lists we have to admit that the future is uncertain, there are upsets all the time, and we need to reward actual wins rather than just projecting into the future. No matter how good a guy LOOKS, he has to have done it to be #1.
So, for now, we'll eliminate Cain, Jon Jones, and Frankie Edgar (I know Frankie technically defended his belt once already, but I have no idea what do do with him and Gray, so I'm dropping them both for now).
The next question is how you rank guys outside the UFC. Mainly we're talking about Gilbert Melendez and Nick Diaz here (with Overeem in the wings). For me, if you want to be P4P, you really have to be fighting the best. That means Nick Diaz is off the list. He'll get his chance in October to stake his claim.
Gil is a little bit harder, you definitely could make the argument that he's top 10, but (again in my opinion) I can't rank him over Frankie or Gray, let alone GSP or Silva.
So what are we left with? In my opinion, four candidates: Aldo, Silva, Cruz and GSP.
GSP and Silva are the two frontrunners. Aldo and Cruz are less established. They haven't defended their belts as often, and they are new to the UFC. As UFC lightweights drop down, they will have new and interesting challenges. So I think, for now, the choice is clear - Silva and GSP are 1A and 1B (you can make an argument for either one) and Cruz and Aldo are 2A and 2B.
GSP has two losses, both of which he convincingly avenged. He has, in my opinion, faced tougher opposition than any of the other candidates. The main criticism of him is that he is "boring" or "too conservative."
With repsect, I really think those comments are not valid in a P4P debate. They are relevant to who your favourite fighter is, but not who is the "best." I am not saying you have to go pay for GSP's fights or else you're not "hardcore." It's your money and your time and you don't have to watch it if you don't like it. But MMA is a sport, and in a sport there has to be a distinction between entertainment and excellence.
Silva, on the other hand, has a better finishing percentage (at least these days - I for one still remember him clowning around against Cote, Leites and Maia quite vividly). But it's difficult to know what to do with his performance against Sonnen. Do you reward him for the dramatic finish? Or do you punish him for the first 4.5 rounds, during which he was largely ineffective? How does that compare to a fight like, say, GSP v. Koscheck?
I also note that some of Silva's title defenses came against individuals who are now cut from the UFC (Leites, Cote, Lutter). No one GSP defended his belt against has been cut yet (although Hardy and Serra are on the bubble).
It's also worth nothing that Silva went up to LHW and looked absolutely dominant, destroying Irvin and Griffin in the first round. That kind of diversity is important in P4P rankings (although Irvin too has now been cut).
But I put a lot of emphasis on the diversity of your skills. If you can do more than one thing, you can beat anything. On the other hand, if you have weaknesses, your record could be a reflection of who you fight, rather than how good you are. And the Sonnen fight raised a lot of questions. Yes, Silva won, yes Sonnen was on steroids, yes Silva reportedly had an injured rib. But if you look at his record in the UFC, there just aren't a ton of killer wrestlers there. To me, that's enough to put him in the 1B spot, although I'm respectful of those that think differently.
That brings us to Cruz and Aldo.
I think the conventional wisdom here is to go with Aldo because of the perception that he wins his fights much more convincingly than Cruz. But remember, 2 of Aldo's last 4 fights have been decisions too, for those of you keeping track (for Dominick the number is 3 of 4, with the hand injury to Bowles being the lone stoppage).
Also remember that while Aldo did look pretty good in that fight against Hominick, it ended up with him on his back eating some pretty hard shots. Convincing win? Sure. Just look at Hominck's face. But it wasn't exactly Silva/Griffin.
In the end, I would cast my vote for Cruz. Why? First, the quality of his opponents. Cruz has beaten two guys (Benavidez and Bowles) who have not lost to ANYONE but him. That's impressive. And in my opinion, Aldo's wins over Faber, Brown, and Gambruyan are not as impressive in hindsight. Faber is 4-4 in his last 8. Brown and Gambruyan just lost again. And as much as I love Hominick, he's had an up and down career as well.
Second, diversity of skillset. Aldo has yet (as far as I can tell) to take on a really amazing wrestler. Sure, his take-down defence looks strong, but until he takes on Chad Mendes or someone like him, we won't know for sure. Cruz, on the other hand, makes strikers and wrestlers look equally bad.
I note, however, that Cruz looks vulnerable to a certain kind of fighter. An iron-chinned bully that wasn't afraid of getting knocked out could track Cruz down and beat him up like Shogun did to Machida. However, right now, his skills are so amazing that it's tough to know who could challenge him at BW.
You can make arguments going the other way. Aldo looked better against Faber than Cruz did, for instance. Cruz has not finished anyone at Bantamweight except Bowles (and that was via a broken hand). Cruz also mainly wins close (if clear) decisions. The dominant wins like over Jorgensen are the exception, not the rule.
It's interesting how much of this debate comes down to one thing: how important is it to finish fights? What's more impressive, to boringly dominate a five round fight, or to get the crap kicked out of you and mount a dramatic comeback?
Your answer to that question (which is totally subjective) will determine whether you rank GSP higher than Silva, or Cruz higher than Aldo.
For me, finishes are very exciting but sports is about winning, not winning pretty. They are only of limited use in determining who is the "best."
But like I said, that's totally subjective.