IIRC we have owned three microwaves. The first was a big bucks, late seventies/early eighties Panasonic from Sears that had all the fancy bells and whistles and was way smarter than either of us (much like every other electronic thing we own
). One day it quit (under warranty) and we called the Sears repair man to fix it. It turned out to be a simple part replacement and while the guy was there he told us that there were few things that could go wrong on a microwave and as long as the Klystron, which generates the microwave was functioning all the other parts were easily replaceable... and Klystron failures were very rare. We hauled that thing through three state side moves and then to Turkey and Italy, where it ran on 50 cycle power on a converter, then back to the states, where it turned out to be too big for the space in out present home. It became my garage microwave and sits under my bench...still going strong...where I use it to dry wood/herbs, warm coffee and, when the kitchen unit is swamped, warm foods when we have lots of company. Our present cabinets have an over the counter space for a slide in microwave which dictates the size of the unit we can use. When the Panasonic wouldn't fit we "temporarily" used the very small, cheap college dorm type unit I had in my office at work...for about three years. Then we acquired the present user, a large GE that we inherited from the MIL. It's probably 15 years old, but it fits the cabinet space and is still going strong. It has simple controls that give from 30 seconds to 5 minutes @high power with the capability to add 30 second increments. You can also set a timer for longer cooks and defrosts. When defrosting, it beeps half way through and tells you to flip the food over. It has more capabilities, but we have never explored them.
Things that are important to us are simple, well lighted controls, ease of cleaning, removable turntable, good defrost capability, interior space large enough to hold my wife's big square casserole dish, and overall size able to fit in the available cabinet space. Beyond those features we might be tempted to get one with convection oven capabilities because we regret cheapening out and not installing double ovens when we built the house.
Out of curiosity I checked CR for recommended large counter top units and Panasonic and GE are still players with recommended units in the $200-$300 range. I know there might be advertising bias there, but it's a start.