I really like concave keyboards, and maybe someday I'll invest in one (I previously used a Kinesis 2 but the company kept it when I left).

But besides the brief Kinesis foray, I have used the MS Ergo Sculpt since...2014, I think. It's honestly pretty nice, especially since I don't really care about mechanical keycaps and I value portability. (The only portability downside is that I need to manually put something in the battery compartment to keep it powered off while traveling, because for some reason it has no off-switch.)