The answer will vary depending on how you expect to use the reader, how little or how much you expect of other functions, what your patience is with not-quite-there technology, and whether you have friends with readers with whom you'd like to share books (among other things). Do read the Sept. 2011 Consumer Reports comparison of ereaders. Then update yourself on the features of the newest Kindle release (which came after the CR review). Also, see http://news.cnet.com/kindle-vs-nook-vs-ipad-which-e-book-reader-should-you-buy
You don't say why you're looking for compatibility with Digital Editions. Most ereader users don't especially care about the reader software, except insofar as it causes usability issues.
Owner of Original Nook, & Color Nook & user of Kindle for PC and frequent user of OverDrive ebooks from public libraries.
I'd like to add a couple of points to these ideas.
Determine whether features such as backlighting, long battery life (even
when turned off), scalable fonts, and compatibility with other sources than
the manufacturer are important to you. Ereaders from Amazon (Kindle),
Barnes & Noble (Nook) and SONY to name three may be so tightly connected to
their respective websites that you may be forced to obtain all of your
ematerial from them (Amazon in particular). Adobe Digital Editions is
designed to be more 'open source' - that is that ADE supports a variety of
ereaders, based on how they handle certain industry-standard formatting
features and digital rights. If you want to download ebooks from the
widest possible spectrum, or if you'd be just as happy with the services
from your ereader's manufacturer, then you'll be able to make the right
choice for you.