Here's my opinion on ALL the current-gen gaming platforms excluding hand-helds:-
PS3 - Similar gaming crowd to the 360, but aimed more for the hardcore gamers with most of its exclusives. For hardcore gaming, this or the 360 will do fine. PSN is free, robust, the store has plenty to offer, but is just lacking in features. Hardware is powerful, but then difficult to code for. However, put a lot of time into them, and you get gems like Ratchet and Clank, Uncharted 2 and LBP. However, no PS2 backwards compatibility with newer models, but PS1 games still work.
Xbox 360 - Simular gaming crowd to the PS3, but more about the slightly casual crowd with its exclusives. Again, hardcore gaming is good on this or the PS3. XBL Silver is free, but no online play. XBL Gold costs, but is a great service with many features, and the Marketplace has tonnes of stuff, even full games to download. Hardware isn't as powerful, but is very easy to code for and port from/to PC, and backwards compatibility is still supported. I've not played many exclusives, but my favourites are ODST (kicks Halo 3 in the bollocks, in good way), GRAW, and Halo 2 for the original Xbox is still fun.
PC - The possibilities are endless really, that's all I can say. However, you must A) have impecable co-ordination to work all the keyboard controls, and will have to shell out LOADS for a good gaming PC or laptop. However, they're useful for more than gaming. Some games even allow signing into Xbox Live.
Wii - For the casual crowd. Games can be fun (Super Mario Galaxy was great) and if you know what to do with it, you can play more games than are released (as long as you don't update). I know this isn't what you're meant to do with it, but playing Quake on the Wii is amazingly fun.