Based on focal length alone I would go for the 24-70mm Nikkor, that should give you damn good image quality and would cover you for pretty much everything that your new lens is too long for.
Primes (fixed mm as you put it) are fantastic in terms of sharpness and depth of field, but will limit you in certain situations. If you're still pretty new to it all I doubt very much that you'll notice the quality difference between a prime and a zoom, so I would go for the zoom for flexibility
