Are you asking what brand do we use, or what brand we prefer?
I use a Sharp, but I don't have a particular preference for that brand of Microwave, it's just the one I bought at the time and it still works.
It's OK, it does it's job adequately and has a nice "ping" when it's done, but I wouldn't recommend or not recommend it to anyone.
I think you'd have serious domestic beast to actually develop a brand preference for Microwaves, those things last for ages and are pretty much the same (I've never had a Microwave that's broken, they've always still worked even when we've thrown them out because they're too grubby).
How many Microwaves could one person conceivably get through in their lifetime? I can ever imagine using enough different brands to ever develop a preference... someone may develop brand loyalty to a manufacturer of Microwaves because of their other products, like if someone had a good Samsung TV they may also buy a Samsung Microwave, but I doubt anyone could develop a preference solely for Microwaves through normal, everyday domestic use.