I'd use a Android tablet.
Personally, I use my n900 for all my ebook-needs, and it does the job quite well - It fits in my pocket, and, (provided I have the font big enough), it's not a strain to read.

Really, the problem comes down to how you are going to be acquiring ebooks - You need to figure out what formats are avaiable at the source(s) you are getting them from, then make sure they are either natively readable, or have a converter.

For example, Microsoft .lit files can be converted to .html files which can then be read with FBreader on my N900 via Convert-LIT. .doc files, which are popular with online authors, can be converted to html or other formats for reading, though not in batch quantity(at least, not that I've figured out).

Once you have DRM in the mix, things get even more confusing, and some formats can be easily stripped and converted, while others (like PDF-ebooks) often cannot. Getting DRM-free content is possible from some authors, though for others it requires shady methods.

The Kindle, on the other hand, is very simple - You buy the book and things Just Work(TM). However, you have -one- source for your books, and can't just load any content you want on it. Nor can you back things up, so if you lose/break your Kindle, you are screwed.