Almost all ebook maker use E-Ink technology. It is E-ink corp control the latest technology; hence there is almost no different on E-ink display as long as maker use E-ink latest technology.
Differences to consider:
1. No. of formats supported - PDF, TXT, HTML, DOC, RTF, LIT, WOL, CHM, Mobipocket
2. Languages - Chinese, English, Japanese, Korean, Arabic, All European Languages
Then - you should look for Genuine Ebook maker, like Hanlin V3