We are considering purchasing a new microwave, so I dipped my toes into the review-water earlier this week. The Wirecutter folks have done an interesting job of disassembling the microwaves from many brands and visually demonstrating that they're all made by one manufacturer. Unsurprisingly, when they test them, they all perform the same, too:
When I was looking for a microwave, I went to an local appliance store because I didn't wanna go to Home Depot etc and get some piece of shit. They told me the exact same thing and that's why they didn't have a huge selection. They basically told me pick the one that looks the best, they all had the same 1 year warranty and same internals. I wasn't gonna get an actual high end microwave without going commercial.
https://www.nytimes.com/wirecutter/reviews/best-microwave/