Whatever is comfortable for you, honestly. Mine, after some trial and error, is 33".
Suggestion - deliberately make your bench high. Use it for a while (not just one small run of ammo). If it's OK, fine; if not, take an inch off. The point is not to be too hasty in trimming. You've got the rest of your life.
Welcome to the dark side.
Edit: Other suggestions
Lighting is critical. If there's some way to build in lighting, it's worth it.
A fire extinguisher nearby (but not right on it) is a good idea. You only need it when you really need it.
Think in advance about how you are going to level it. I'm not saying that the tabletop needs to be perfectly level. Rather, if one leg is a bit too short and the bench wobbles a bit, how are you going to fix that annoying problem? (In my case, I put 2x4s horizontally between the front and rear legs. I have an unfinished concrete floor, so a lag bolt screwed in from the top of the 2x4 allows semi-precision adjustment - good enough, anyway).
A raised platform for beam-balance scales is a very good idea as you don't have to scrunch down to read it. The plans chalkriver linked to put the scales on a shelf - same-same.
Painting the top white or covering it with white Melamine makes cleanup much easier.
A strip magnet fastened to the wall is an excellent place to hang fiddly tools like Allen keys, tiny screwdrivers, etc.
Nearby storage space for the dozens of little bits and pieces - dies, stuck case extractors, lube sets, bullet pullers, etc - will save you a lot of time. I have a cheap set of drawers under my bench and a discounted cupboard on the wall above it.
