PS3 - the hardware isn't a bit better than the 360, it's a lot better. The Cell BE when properly utilised... well. It's scary-fast.
As far as I can see though, it looks like most of the PS3 exlusives might not be as exclusive as one might think: The only "big name" titles I can think of that we were promised that are still exclusive will be MSG4 [which may still go XBox, I know the last two did] and GT5.
Also, you probably won't have backwards-compatibility with the PS2 unless you get an MGS4-special-edition pack.
As for the 360.. well it just came down in price again.