The 50mm will produce technically 'better' photos, they will be sharper and you will be able to use faster shutter speeds because of the larger aperture (or shoot in lower light)
However, for a noob, the 28-70 will give you more options with regard to composition and framing etc. The 70 end also compresses perspective and is preferable for portraits as it produces more flattering results.
Any help? What sort of photography are you planning on doing?