Always 2 seperate ones MWs do not last forever . In fact I do not like buit in MWs at all since usually about the time the MW dies the size you had is no longer available . A shelf for the MW or even on the counter is a better choice IMHO.

Patricia Colwell is right. I learned this the hard way. The attached mw fizzled after two years. Too expensive to repair, so I lived with a dead mw for another 15 years, waiting for the oven to die.

Buy the micro first and have a shelf built for it. My micro broke down in the first couple of weeks and was replaced under warranty.

Buy separately. Our ca. 1985 GE Micro/oven wall combo lasted a long time,. Then the microwave stopped working.

Same thing happened to friends after 20+ years, both houses built around same time. (probably same model) Friends replaced with another microwave/wall oven combo, but the cutout was different and that complicated things, requiring some cabinet adaptation.

Ours triggered a massive kitchen remodel in 2012 (much needed, but I digress) and we decided to have a separate cubby/shelf for the microwave, which has already been replaced once after eight years. Even the kitchen designer suggested a separate cubby for the microwave.

I have a wall oven and a microwave drawer.

The oven is Bosch and the microwave drawer is Sharp.

At least for me this is the perfect combination as the oven is perfect height and is also a side opening model which increases ergonomic functionality. The microwave drawer below is also highly functional - like you I use the microwave much more frequently than the oven.

I have a large storage drawer below the microwave as well as a cabinet above the oven with "slots" of various widths and so it holds an incredible amount of "oven" type of cookware including a large roasting pan - all much more readily accessible than if they were stored where they had to be stacked.

Separate, more likely the microwave goes out before the oven.  We just completed our remodel and had a GE cafe wall oven with GE microwave wall mounted above with trim kit to match.

I totally agree with Patricia Colwell about installing a microwave shelf in your kitchen. When I had my galley style kitchen renovated a few years ago, I included a shelf (25.5” wide and 22” deep) for a microwave. My current microwave is 21.5” wide and 18” deep.