I suppose it depends on which country's games you like more. the Playstation has always been home to the never-ending flow of Japanese games. If you find Japanese games tantalizing, I'd go for a PS3. However, most American and European developers realize the money in making multiple ports (in time, of course). Therefore, if you are a fan of American made games (specifically PC ports and FPS shooters), then the XBox 360 would be a good choice.
All in all, though, you're going to miss out on some games, period, unless you have ALL of the consoles. I bought a Gamecube specifically for those off-the-wall games that are made for nintendo (and Mario Kart, baby!). If you are a PC fan, then it's a toss up... you'can have PC and PS3 and miss very few exclusives. If you want to rely more on your consoles, I guess the XBox 360 would be a good selection (as a "replacement" for your PC).
Me, I started with an NES, then went SNES, PC (and have been upgrading ever since), PS1, PS2, XBOX, GAMECUBE. I won't buy any of the new consoles until they're at their rock-bottom price, because the best games ever made have been made for the PC.