I just got my Sony PRS-600, and I have to say I'm very happy with its PDF handling. It does text reflow and zoom, and you can also switch to landscape mode, which works well with larger PDFs. And the build quality is exceptional - a really solid metal casing with just a few simple buttons. Yes, the screen is a bit glossy, but I'm so used to the high-gloss look of a Mac laptop screen, the Sony ereader seems quite matt in comparison.
Admittedly the pre-formatted US letter sized PDFs I have are mainly text (course materials on fiction writing), but even with my dreadful eyesight, I find them quite readable as-is in landscape mode. I guess with large or detailed images you might struggle with a 6" device, but the choice of bigger screens is pretty limited. If you're in the States or don't mind buying from overseas, you might want to look at the PRS-900 (it's not available here, so I didn't consider it).
The PRS-600 also plays nicely with Calibre - better than the Sony software, at least on a Mac. Epub conversion "just works"
Downside is no WiFi or 3G, but I can live with that. They just suck power, anyway...