I like to put it below counter height in place of a deep drawer in an open cabinet. The backside of an island is ideal. It's accessible to everyone and out of the way. I hate taking up counter space with them.
If you use it often, make the microwave part of a built-in at eye level in a deep cabinet space above the oven. If not, I like to include it on the counter but in a small appliance cabinet that can be closed and hidden with a roller door or recessed panel door.