Microwaves suck when mounted over the range. They're easy to see, and it's easy to get things in and out, but they make shitty range hoods, and they're in the way of everything that you might want to do on the cooktop. Hate 'em. Best option is mounted at ~4'-0" AFF in a full height cabinet. Second best is undercounter.
When I retro-fitted my kitchen and replaced the range hood with one I actually disassembled the cabinet and cut it down to make sure that the microwave would be high enough. I think a lot of the time people swap them out and just give up the space.