I have used both, it depends on what you like.
A difference is that walnut is about twice as heavy, that also depends on what you want.
A suggestion or two
If you decide on the maple get tiger stripe and use triaminic acid to stain it and tung nut oil to finish it this not only traditional but the easiest to take care of and by far the best looking. Walnut is kind of dull looking so it is good looking with a hard shiny finish. If you want some thing colorful look at Birdseye maple triaminic acid will also bring the color out in it. I used to custom build and will try to answer any questions.