1) Sony PRS-505The "Classic" and the absolute winner among all the readers since sales began. But it is no longer manufactured since 2009.
2) Pocketbook 301+
The company pocketbook began its triumphant climb with this model, and so they captured 2nd Place in the rankings.
3) Pocketbook 360°
The novelty of the year 2009! Pocketbook 360° could prove a better place if the price is not with the "classical" 6" models would have been comparable.
Bear in mind that the above list is representative of the Russian market where the format requirements are different than most of the other countries. For instance, ePub is not popular in Russia, they mostly use fb2 therefore devices that don't support fb2 probably lost points during the comparison.
By the way, check this page if you want a quick guide to e-Book formats!