If you are planning on makng music like Hip Hop. And its only you, hence you will be recording max 2 tracks simultaneausly, then I would say go for the Laptop because of the portability.
But if you looking at recording alot of tracks and working with vst's and tons of effects for every track, then id go desktop.

Do you have an idea what program you are looking at?

Ableton live will work real nice on a laptop.

Whereas cubase sx3 with all the vsts would be better on a desktop.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
black dante