I know there have been a lot of GSP vs BJ threads, but none were for the purpose of who you think will win. Sorry if I didn't see it.
Anyway here is how I see it IMHO.
I think that BJ is going to win in round 3 by (T)KO or round 4 by submission. The reason I think this is because BJ is the most naturally talented fighter in the world. Plain and Simple. He was once the WW champion relying on natural ability with hardly any training at all.
We have finally seen what BJ is capable of in his past 3 fights. He has dominated every single one of them without being in trouble once. He is re-focused or maybe focused for the first time solely on fighting. I personally think their is no stopping the guy.
However if GSP can take BJ Penn down it will be a whole different fight than what I'm thinking. I don't think Georges can though because in their first fight if my memory serves me correctly Georges couldn't get him down until the later 2nd round and all of the 3rd round, and that's because BJ was tired. I think BJ has the best TDD in the game.
We all know that BJ can outstrike GSP, and if you don't know that go and watch their first fight. I don't think a lot of people realize how good BJ standup is. He is one of the most calm and collective fighters I have ever seen. IF he gets hit then BOOM!! He just side steps it and re-collects himself. I have never seen BJ get over exited.
So with no more rambling from me I think that BJ is going to win this fight in the 3rd or 4rth round, and if he does I don't think you can deny him the p4p best fighter in the world!