1. ePub support. I currently have a Sony 505, which supports ePub, but I thoroughly dislike the way it displays ePub files, especially when the font size is increased. I don't think I'll be buying another Sony device.
What bother you ? Lack of hyphenation ?
If so, the only ePub reader I can think of that have hyphenation support are the pocketbook, when using fbreader. But fbreader hardly support css.
Margins, I "fix" the problem by editing the ePub. A bit anoying. Not sure if any reader support that.