I have a Logitech NewTouch Compact. You can't actually get them anymore, but it's more or less like their Cordless natural one, it's about the same size and shape, but it has no internet/mm buttons like the cordless and it has a cord.
It's an ergo, with solid clicky buttons, no extra mm/internet buttons, and it's fairly small (for an ergo).
I like the logitech's better than MS becaue the logitechs are solid and clicky, I like that better than soft and quiet, but that is 100% personal preference, neither is "better quality". I find the clicky keys easier on my fingers, but that's my opinion. My roommate hates the clicky keys.
I like the full size MS Natural Pro, because all the extra keys are arranged normally Home,End,PgUp,PgDn,Insert,Delete are oranized funny on the Logitech, I like it better once I got used to it, but it is different...the smaller MS one has the arrow keys arranged funny...the full size MS one has normal Home,End,PgUp,PgDn,Insert,Delete and normal arrow keys. And the MS one has a 2 port USB hub in it (this of course only works if you use in USB mode, and notin PS/2). But the full size Pro one is expensive and I like solier feeling keys.