I've been doing a bit of both recently, scanning negs & slides my mate took years ago. My findings are, if the neg is dirty, the dust/dirt is enlarged the same amount as the image so you must make sure your neg is spotless to start with. When printing a scanned neg, you are enlarging it quite a bit.
I have been scanning 6x4 prints and printing to the same size and they've been fine. Again, watch for dust on the original.
I am using a basic flatbed scanner but there better options out there I'm sure.