Honestly, neither lens is brilliant.
The 24/2.8 is one of the oldest Nikkors still being made and has some real problems, even on an APS-C sensor. The only thing it has going for it, really, is that it is very compact (and it's $2000 cheaper than the f/1.4 version). It is fairly soft by today's standards, and suffers from considerable vignetting wide open, pretty substantial lateral chromatic aberration, and some curvature of field that may or may not be problematic depending on the kinds of images you're shooting. It's really time for Nikon to update this lens, but they may see the photographer's choice as being between a zoom and their much more expensive fast lens.
The old 24-85 has been discontinued for years in favour of the 24-120, but if you can get it at a reasonable price, it's a better lens than the 24, except for a bit of extra barrel distortion compared to the prime. It's considerably more bulky than the 24 as well. It's not as good a lens in a lot of respects as more recent designs, but at the same time it is better-behaved than the ancient 24/2.8.
The newer version of the 24-85 (the one that's likely to be the "kit lens" on the low-cost full-frame D600) would probably be better in most respects (it's a new design with 16 elements in 11 groups as opposed to the 15 elements in 12 groups of the old lens) and has VR, but it's a little more expensive and, being new, will probably be hard to get for a little while.