I own both consoles, and I would say definitely go for the Xbox 360.
I love them both, but the 360 has a lot more exclusive titles (That I want to play) than the PS3.
Xbox 360 (Fable, Gears of War, Halo, Crackdown and Mass Effect)
PS3 (Little Big Planet , GT5 , MAG)
Its worth making a list of the games you want to play for each console, and choosing from there.
I would Also note that I find the Xbox Live experience to be a lot more enjoyable than PS3 network. There seems to be a lot more content on Xbox Live, the Headsets are more comfortable and if most of your friends have a 360, then it will make your gaming experience more enjoyable too.
I've never played online with a friend on the PS3,
1. Because nobody I know has one
2. Because the headsets kinda suck beans
3. Occasionally there is a slice of lag
If your thinking of getting a PS3 for Little Big Planet, its only amazing really if your playing with friends ( and they are in the same room). Considering only one of your friends owns a PS3, you may find your not playing online as much, and it tends to get a little old... fast.
However, the PS3 is a little more "Mature" than the 360. With a PS3,
1. You can Upgrade the HDD as you please (with standard Laptop SATA drives)
2. You can use Game Saves from the internet with just a usb pen drive
3. You aren't forced to but Sony only Hardware (For instance the charger cable is a standard USB-USB mini cable)
4. The Dashboard is faster
5. The Controller includes an inbuilt battery (non of this play and charge kit nonsense). The controller is also quite a bit lighter a result.
6. (A strange one to add maybe) But the PSU is built into the console. The 360 has a large square block attached to the power cable (Which magically gets cut out of size comparison screen shots). Which also brings me to mention that the Power cable for the PS3 is just a PC power cable. (Again non of this Microsoft manufactured only thing)
Also with the added bonus of BluRay support (Although there isn't much point in BluRay if you haven't got a HDTV)