I guess you live in the USA? Your choices are probably the Nook, Sony Readers, and the new Kobo.
The Nook can also read EPUBs. None of them can read LIT, as far as I know, though the format is easily converted by
Calibre.
Does screen size matter to you? Form factor? The Sony Readers have the newest Pearl e-ink screens, meaning the darkness of the text is much improved. Some people notice a difference and prefer the newer screens, some don't.
I can't speak for the Nook, but I have a Sony Reader 350. I love it. It's fast, compact, and handles PDFs very well (though my PDF use is limited to novels published in that format, not technical PDFs). Lack of wifi isn't a downside for me at all, but I have my reasons -- others would regard the wifi as essential. The touchscreen is very responsive. Build quality is solid. The few bad things I can think of are that the Sonys are considerably expensive compared to other ereaders, and the 350's 5" screen may be too small for some unless one's willing to spend extra for a 650. If you really do have a billion books and would be using a memory card, you should be considering the 650 or 950.
There is a new Kobo coming out very soon, I believe, which means nobody has any hands-on experience with it. (It should be significantly improved over the old model.) Still, it's worth considering.