I would go with PS3
I have an xbox, but only because I got it cheap. I would recommend getting a PS3, but here are the facts.
The best selling console is the Xbox 360, therefore most of your friends, and just more people in general will be online.
Microsoft will nickel and dime you. For example: you have to change your name, download themes or icons, map packs, cables, etc.
Once you buy a PS3, except for games, your pretty much done with paying. You get free online play (unlike xbox which is anywhere from $50-$100 per year.)
It is predicted that 25% of xboxes purchased this year will get the red ring of death, not so with the PS3.
The Xbox is about $100 cheaper.
I personally like the Xbox controllers better. But the Duelshock 3 do have motion sensors.
The PS3 has better graphics. Even if you do the HDMI thing on the Xbox, it can't play Blu-Ray like the PS3.
You get the dashboard on the Xbox 360, which includes MSN, Netflix, the ability to download games, etc. There have also been rumors about facebook and twitter integration.
The PS3 has a web browser.
They both have great games, but one could argue that the Xbox has better games because of games like Halo.
So financially (if you plan on playing for more than a year) the PS3.
I will let you figure out the best.
Buy the way, that can be a really dangerous question, Xbox fanboys can be vicious.
For anyone who cares, I only play COD4 and I'm uPaymeiFixit (@live.com).