The MS ergo keyboard isn't wide enough for me but I'm not against a one-piece design. I just recently switched to a Kinesis Advantage2 (split-but-one-piece) at home but I have a straight two-piece keyboard at work. The width I keep the two-piece at is a bit wider than the Advantage but it's not enough to bother me.

>If the latter, what do you like about them?

The main issue for me is that I'm 6'6" and have broad shoulders. Normal keyboard layouts cause me to roll my shoulders dramatically so I can get my hands on the home keys. This caused some shoulder pain issues in the past when I had code-heavy weeks. Split configuration seems to have fixed that completely.

Single piece split keyboards still restrict the angle of your wrists. I find the MS ergo keyboards to better by default, but having the ability to adjust the angle opens the possibility of finding an even better angle (that may change over time).