Well, the PS3 is the GameCube of this console generation.
The PS3 is suppose to have the technical superiority, but without the market share, a lot of games are getting ported second to the PS3, from the Xbox (For the PS3 case), so any thing the game may have benefitted from being on the PS3 is lost, beside the last minuet tacks on with the ps3 controller things.
Though the PS3 doesn't make porting easy from my understanding, as the console is suppose to be rather hard to program for.
The free on line service, I dont consider to much of a Pro, as in my experience, the user experience with X-Box, is much more polished, and User friendly. X-Box Live, really doesn't cost that much if you buy it for a year.
The PS3 does have much stronger backward compatibility then the X-Box, but I find this understandable with the X-Box, as its previous console library wasn't as strong or as diverse as the PS2. It would have been a much stronger weakness on the PS3 if it didn't have the backward capability.
I much prefer the snap in hardrive for the X-box, then the PS3 set up. Even though the I find the hard drive to be overpriced, but the ability to upgrade later if you want, and the ease at which its done, is quite nice. Though I do think its bull shitty that the hard drive transfer cable doens't come with console. (But I'm not a 100% certain if it comes with hardrive purchases.)
The PS3 control, is lighter, in my hands, but I dont find either first party controller to be stressful to hold for hours.
Uh...
Lets see. The PS3 can do Blu-Ray movies, which I think is a point in its favor, but no wear near as strong as the DVD movie functionality in the PS2 was.
And 3D Games. Sony is totally gun ho on 3D tvs and games. I dont know. I'm not that excited by the 3D TVs, games or movies really.
So yea, um.
360. The game library, I dont consider as diverse as the PS3, however, when I've gotten the chance to play 360 and PS3 ports, the 360 ports seems to be better in overall production and user experience.
I dont think one better then the other, but if I were to buy one over the other. I would choose the 360, as its to me is the better supported console.
Though I still want a PS3.