My favorite keyboards is the Microsoft Sculpt Comfort. I can type for hours without any wrist pain compared to all my other keyboards.
It hits sweet spot - it is slightly curved but not to the extreme where one would have to re-learn how to type, battery also lasts extremely long. Only issue I have with it is that additional functional keys switch is literally a switch, one needs to change its position to be able to use alternate keys function - for me it would be more convenient to have "Fn" key just like in notebooks keyboards.
Edit: oh and maybe another one - missing physical switch on the back to disable keyboard, now one needs to remove battery or put some scrap of paper/plastic between contacts to completely "power off" device.