Welcome Janiceoc. We all have opinions and desires. IMO none of the readers are perfect so it depends on what you want the most, how computer savvy you are, what you want to read and what formats they are in.
The Kindle is great for easy purchase of ebooks from Amazon and with some work on your part can easily read DRMed Mobipocket ebooks as well as unDRMed Mobipocket (with no extra work - I think - don't have personal Kindle experience).
The Sony also has their own proprietary format that can only be purchased from Sony. But they also have an unDRMed version that has become more widely available and the new ones can read epub format.
Bookeen's Cybook Gen3 (and the Hanlin V3 family - includes BeBook & EZ Reader)reads bothe DRMed & unDRMed Mobipocket ebooks and there is a wide market for them. Cybook has dictionary support and excellent font size ability (Hanlin slightly less font size ability with their native firmwares)
This just brushes the surface of some of the 6 inch readers. I like my EZ Reader but with the open source firmware called OpenInkPot (or OI). OI doesn't read any DRMed formats but reads several unDRMed formats.
Most of these readers say they also read PDF (unDRMed). However PDF is much mor problematic and I'll leave it at that for now.