I have both, and I've had them for a few years, and I honestly have to say (hold up flame shield) I've generally preferred my PS3. Functionality, free online features, and some very, very good exclusives. Don't get me wrong, I've loved some of the Xbox 360 exclusives, especially Mass Effect (though that is also on PC, and my PC could handle it, so I wouldn't be missing out much if I didn't have a 360).
I also found Xbox Live to be a frustrating experience, due to the adolescent nature of the players, so I cancelled my subscription. PS3 also feels like it has a lot more evolving to do, I mean it's the only console with Blu-Ray support, and you can tell this is made fantastic use of with exclusive titles (such as MGS4, God of War 3 and Uncharted 2).
Also, I don't know whether this will clinch it, but I'm also a big PC player too. RPG's and FPS games, just like you.