This is a tough one. Without sounding biased and slanted (which I am anyways):
I tried Cakewalk for awhile, but found it too buggy for audio recording. Too many random stops while playing or recording. This was the main thing that set me off Cakewalk. That and too many memory leaks ala GPF's/illegal operations.
Cakewalk works for many people, and I have no doubt it's a great program. I've heard many times that Cakewalk is easier to learn than Cubase, but I don't really find that.
Cubase is not perfect either. Far from it. It has its share of bugs, but not as many, and not quite as annoying as the ones I encountered in Cakewalk.
The other reason I use Cubase is its support for ASIO. This allows faster response within the program, move a fader it adjusts the volume almost instantly etc.
Try the demo's of both and base your decision on your own experiences before you plunk down any cash.
Emeric