With music, assuming we ignore the difference in price Mac or PC comes down to a) what do your mates have and b) what software do you want to run on them. If you wanna run Logic Audio or Protools I'd go with the Mac, if you are running stuff that was developed with the PC in mind then go with the PC.

Laptops are funny things though ... relability becomes a new issue. I've had three in the past four years (PCs, Toshiba, Fujitsu, Dell) all of which have died of some kind of powersupply/battery/general rebooting problem and I don't even take them out of the house much. Luckly work pays for them.