So you have asked a trick question. Quality and microwaves are not words we use together much.

That being said, the Jennair units use perimetric venting, are a little deeper than the norm, and have a 400CFM blower. Those things SHOULD make it vent more effectively…should being the important word. As for cooking goes, microwaves all come out of a small number of factories, so I doubt you will see dramatic differences in that arena.

we have a 10 year old panasonic genius prestige. It vents very well for an OTR when you use the extra high setting. We've had to have a couple of very minor repairs in the 10 years. I have no idea if it is still as well made as it was. I bought it on the advice of my mother in law who bought hers a year before mine (hers lasted 9 years and then died), my sister in law got hers a year after us and it is still working. I've since heard that having an OTR last more than a few years is rare. When you do need to fix them, you have to get someone out as it is hard to remove them.

They are all pretty much the same. I find it hard to believe--actually impossible to believe--that you would get 400 cfm out of a Jennaire mentioned above. You are trying to squeeze blower power into the tight space of a microwave. Furthermore the ducting of OTR MWs tends to be 3", again making it impossible to exhaust effectively. Then you have your issue of coverage or capture area which is not much more than over the back burners , with just a couple of squares in the bottom of the MW. Then you have the noise issue - there is no OTR MW made that is not extremely loud.

There are several other problems with OTR MWs. If you have no other choice due to space constraints, that would be the only reason to choose a OTR MW over a hood. In that case, don't spend a lot of money, cause they are all the same and just made by 3 manufacturers, despite all the brand names you see.

JENNAIR OTR

Thats the unit in question. While your points are valid, this SHOULD vent better than others. I won't say it's anything close to what a hood is, but the layout of it (17" deep) and the perimetric venting alone should work more effectively than a traditional unit.

Thank you all so much for the help! Would anyone happen to know which of the 3 manufactures is the best, or what lines they each make? For example, it sounds like whirlpool makes kitchen aid etc. We are replacing an already existing microwave in a kitchen with little counter space so pretty much have to stick to the OTR even though I know that a hood would be better for venting. Thanks so much!

Whirlpool owns Kitchenaid, and Jenn Air for that matter. Who they buy from is unclear.

Check out the LG models with extends-vent.

i have this one.

http://www.homedepot.com/p/LG-Electronics-2-2-cu-ft-Over-the-Range-Microwave-with-Extenda-Vent-in-Stainless-Steel-LMH2235ST/205192744

Whirlpool/Maytag/Jennair/Kitchenaid/Inglis company generally gets theirs from Sharp. GE makes their own and will probably take over production of the Frigidaire/Electrolux models now that the companies are merging. LG makes their own, and and has made some for some others, notably GE in the past.

In a small kitchen, I generally recommend the GE Advantium OTR model so that the kitchen can have the convenience of the extra speed oven. The venting isn't any better than any of the rest of the lot, which is to say, they are all poor at venting. But better than nothing.