Interesting to me you say this, as my main criticism of most ergo / split keyboards is they don't have enough keys on the thumb. I started with a Maltron [1] with 8 keys on the thumb and that seems a good arrangement to me.
I was at University, doing a lot of typing, and complained about wrist pain. The IT dudes pulled this dusty old Maltron out of storage and gave it to me. Once I got used to it, I loved it, and Uni let me keep it when I left. I unfortunately had to stop using it because it had a PS/2 connector, everything was moving to USB, and I couldn't afford a new one at the time. I'm hoping my current keyboard (MS Natural) will finally die so I can justify getting a new one.
I haven't used a Kinesis, so can't compare to it (though Kinesis is supposed to have copied their design, so I guess it's very similar.)
I agree, I think the kyria, lily58 (and its derivative lotus58) are decent options, though the BFO9000 could also work as the ultimate split keyboard haha