I was actually considering all 3 (plus the large Amazon Kindle DX), as I was looking for a large screen ereader that's easy on the eyes (i.e. e-ink).
Pretty much ALL the large 9" e-ink devices are around the $300 mark, none are cheap (which is probably why the market isn't too big for it at the moment).
Jetbook Color
I initially wanted the Jetbook Color. Yes the colours are muted and not too varied, but that was more than satisfactory for me (being the only commercially available colour e-ink device outside of China afaik).
But after seeing enough pictures and videos (including those which AREN'T under a floodlamp), I eventually decided the (grey) background was too dark to be used in variable lighting conditions in a country that isn't too sunny (if I was in a hot/tropical country I'd be all over it, but here I don't want to be looking for good lighting all the time). And having good contrast/less eyestrain is the primary reason for going e-ink in the first place.
Amazon Kindle DX
This one uses the excellent newer Pearl screen (pretty whiteish), which is fantastic. But seems to be lacking a little functionality (no touchscreen, and other things), and is very out of date/unsupported/abandoned by Amazon, hasn't been updated since 2009! (so very risky to buy)
M92 and Pocketbook (902,912 etc.)
On the other hand the M92's firmware has recently been updated (and hopefully will continue to be so), a lot of help/support provided (thanks to Booxtor especially), and seems to be the least buggy of the lot?
Pocketbook may also boast those two qualities, although I haven't researched it too much.
There are plenty of Pocketbook 912 vs M92 side-by-side
videos, and in my opinion the M92 screen looks better (and I later learned M92 used Pearl e-ink screen, whereas Pocketbook used the older Vizplex), and seems a bit faster for performance. SO winner = M92
I've just ordered a M92 (black body version, to give my eyes the perception of the screen being even lighter than it is) and will see how it goes.