I did a LOT of research before buying my 'next-gen' console.
I bought a PS3.
A huge part of this is personal preference. That's what will win the console war - what genres are more popular.
I, personally, can't stand FPS. At all. I find them tedious, boring, unimaginative, condescending, and way too easy. I have great twitch reflexes, which saves me in a lot of games, but I prefer to think my way through things. Thus, I tend to prefer RPGs that have complicated character development / combat systems, where foresight can turn my dinky little guy into an undefeatable monstrosity. This makes most RPGs easy for me, too, but at least they aren't boring about it. Action games, which usually require either twitch gaming or finding a long and complicated combo and then spamming that ad nauseum, play to both of those strengths (in some cases, at the same time). As a third genre, fighting games always hold a special place in my heart. Not sure why. Maybe it's the actual martial artist in me? /shrug.
So, with that in mind, look at the list of exclusive games on the 360 that appeal to me:
...
..
.
Mass Effect? Maybe?
Yeah, not really worth it.
The PS3, however, has Heavenly Sword, Ratchet & Clank, had DMC4 (it switched to cross, but it wasn't when I got my PS3), Metal Gear Solid, Tekken 6, LittleBig Planet, and quite a bit of setting-favourites. As a HUGE boon on top of that, the PS3 has backwards compatibility with the PS2 - which has a ton of games I really want to play, but never had a PS2 to play them on. I'd be lying if I didn't say I was disappointed with the Guitar Hero backwards 'compatibility', but them's the brakes. At least I can sort of play GH1 on it (as an aside, I found I quite like using a regular controller for some songs, so I should be thankful.)
For me, the choice was obvious. As an added bonus, I got to dehook my old PS1.
For a FPS fan, I can't really tell you what to do. If you are like me, one of the fourteen people on the planet who play games but hate FPS, I would really urge looking at what you'd be getting from the 360.
To show how much I hate FPS's, though, I'll give you an example: I bought Half Life 2 for $20 some time in the fall, and played it twice. Twice. Every one raving about how great and amazing a game it is and I can't be bothered to play it because I hate its gameplay.
I couldn't care less about how what a system can do compared to another. I just want to play games I like. The PS3 was the choice for me. The free online play and the *built in* wireless internet, however - that gets major bonus points. Even if I never use the online play for anything but Guitar Hero.