For prints it really won't matter. you can use most any flatbed. The
control software may not do what you want to do very well. That's where
third party software like Vuescan and Silverfast come in. For negs
it will depend on how much detail you want to get out of the image and
how much you want to spend. For many people, one of the high end epsons
are just fine. To get more detail, and have a higher resolving
capability, a ccd film scanner similar to a Nikon cs5000 would be
appropriate (inexpensive film scanners may not be much better than a
flatbed). For really demanding image reproduction and large blow ups,
nothing beats a drum scanner. It really depends on what you are trying
to do and how large the output needs to be.
regards,