Either use a dado or a router; single saw blades take too long and every time you move the item you increase the possibility of error.
If you use a dado set I'd suggest, (if you have the skill), make a dado sled then you can remove the fence, the only issue with that is accuracy of duplication, (eyes, fingers, pencils and tape measures) increase the possibility of error with each move.
MT Stringers suggestion is your best bet for accuracy and duplication, (if you have a router and the skill to produce the jig) there're many examples on the web. MT's jig allows for both sides to be cut simultaneously, a good thing for time and effort. I have a simpler version of MT's jig; I just cut a slot to fit my biggest template guide, from there I can use pretty much any straight bit from 1/8 - 1" to produce a dado for any depth or shelf thickness "I" could want.
MT is much more adept with jig work than I; with MT's jig you can go mental with all the options.
Work smart not hard!
Never bite the hand that looks dirty