They come pretty standard to fit in a 30″ opening, and height can vary about 1″ depending on the brand. You would want to make sure you have an outlet in the cabinet above as they all plugin today and are not hard-wired. I would make sure proper venting is in place if not recirculating. Options include today a convection mode on select units. So the micro can double as an oven if needed. So the first thing to check is space, 2nd is the venting requirements, then you get into specific features. LG, for instance, has a model with an easy-clean interior and a pull-out visor to give more venting space and a higher cfm motor. It is a unique piece that works very well as a hood, not just a microwave!