Libre has the shortest battery life of the three, and uses the most power. The screen is much less print-like to me (TFT-LCD), but it's still very easy on the eyes.
505 is truly the best of the three, but it's just the matter of finding it since it's discontinued.. If you've found one, go for it.
Kobo has poor support for formats, iirc. ePub or bust, really.
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