Lower end units and all pretty much the same, 1000-1100 watts, generic functions, reheat, potato, popcorn so on. Some have recessed turntable, some not, I prefer recessed. all will have pretty anemic exhaust fans. As you move into the mid $200 range you will find non-stick interiors - a BIG plus in my book, higher CFM fans and a few more options and a bit better build quality. When you move into the mid $300s you can get convection combo units - operate as an oven and a microwave.
I've had 3 or 4 over the last 30 years and liked all of them, never want a microwave on my counter. I swapped out the last one to get a convection unit. I use it , but not as much as I had thought. I keep my old one in the garage and use it occasionally. It had a non-stick interior and they newer unit has stainless - a real pain to keep clean. One thing I strongly suggest is to vent it outdoors if at all possible. All can be set up to recirculate, most offer charcoal inserts to deal with odors, but they have to be replaced regularly and can get expensive.