I've never been able to use a non-split keyboard comfortably for long periods of time. I used a Kinesis Ergo for awhile and generally liked it except that I still have to be able to use other people's keyboards from time to time and it was just too different. The Microsoft Natural 4000 has been my favorite for around 8 years but I wish I could get one with mechanical switches. It has a slight curve - the "flat but split" form factor of some others feels a little off to me.
Mine as well, I'd very much like a mechanical version with the exact same geometry, I even loved the massive removable rest once I got used to it, been able to use a keyboard in a neutral position had a massive impact on my wrist/arm pain (it pretty much went in about 6 weeks between the keyboard and tennis ball exercises).
