Since the game hasn't been released yet, there's no real way of knowing exactly which will we better to play.
What we do know is that the two consoles have pretty much comparable graphics, with the PS3 occasionally getting higher frame-rates but the 360 getting better looking textures.
Due to the slow speed of Blu-Ray drives, the loading times on the PS3 will be longer, but there should be an option within the game to pre-install a portion of the game on your PS3 hard drive. Therefore, the game should be identical in terms of content on both consoles, so odds are loading times will be more or less equal for them both.
In general terms, the games are the same on both systems. That being said, the 360 version will probably be superior. The Xbox Live service is far easier to use and better implemented than Sony's Playstation Network (although you still have to bring the fee for Xbox Live into the equation somewhere) so multiplayer will probably be better on the 360. Additionally, Microsoft paid many millions of dollars to get exclusive downloadable content on the 360 version - which may or may not come out on the PS3 at all. Basically, you're getting the better game on the 360 if you take into account online play and downloadable content. If neither of those thrills you, then they're probably both going to be essentially the same game.
Of course, to know for sure you're just going to have to wait for the game to come out and listen to word of mouth.