Please let us know if these are countertop or over-the-range (OTR) microwaves? If a countertop model, I like the Panasonic Genius Prestige line. Though frankly, no MW these days is going to have a long life, probably 3-5 years is average. But if you've had three MWs all fail within one year, that's really odd.

If you are talking about OTR MWs, those tend to have shorter lives due to the exposure to the heat of the range. But if yours are all failing within a year, and they are OTR, I would say your range is too powerful to have an OTR MW. An OTR MW should only be placed above a range with lower btu's than the "semi-pro" ranges.

Here is a link that might be useful: Panasonic Genius Prestige Microwaves

Do you M/W a lot of Pop Corn?
I've found that frequent popcorn popping is really hard on a M/W. Especially popping back to back bags.