It would seem to me that small size, and lower wattage is the ideal for sailboats. With a common terrestrial household unit that draws 1200 watts, you're pulling 10 amps. If the microwave and fridge are on the same 15 amp outlet, you're approaching or exceeding the 80% safe load of the wiring and the outlet.
You're much safer with a 750, 800 or 900 watt microwave oven
. (Unless you're giving it a dedicated circuit)
I'm talking about small and mid-size cruisers, who are equipped with the typical single, 30 amp service.
As for brand? Any of the well-known appliance makers should provide a long lived unit: Amana, GE, LG, etc. I'd be skeptical of any unit made by a company whose name I couldn't pronounce, and had never heard of.