Although I returned my Franklin eBookman a long time ago because of Franklin's false advertising (don't even go there), I have to say the ergonomics of it were great. In my left hand, the page turn button was under my thumb, in my right hand it fell under my index finger. Either way, just click, click, click. Great one-handed viewing.
I love my Sony 505, but it's not great ergonomically. Oddly enough, it's better in the case than out of it - either the case it came with or my M-edge Executive cover. Either one changes the center of gravity enough that I don't feel like I'm going to drop it, although the ergonomics could still be vastly improved.
The ergonomics of the upcoming Pocketbook 360 look great. Big simple buttons - if the center of gravity is right, that one could be the winner.