I'm still very happy with my Cybook Gen3 (had it for 2 years now). Keeps things simple. It's the lightest 6" reader I think, although this means that it's not as robust, so take care of it. But very easy to hold and a joy to read.
The updated firmware for ePub works well, lots of font sizes to choose from, and an emboldened option.
The pdf support has an automatic crop margins feature which flips the pdf to landscape and gives you the widest view it can on the text itself. This means you can scroll through about a third of an A4 page at a time. The text is tiny but readable, but you won't get any better on a 6" device.
If you want to have the pdf more readable then you can set the zoom manually. If a pdf is formatted in columns this is fine. You read down one side then move back up and down the other. If you want better support for A4 pdfs then you're going to need a much larger reader, and at the moment none of them are really full-sized.