For reading PDF without any kind of preprocessing, the iLiad is the best with it's larger screen, higher resolution, and better PDF reading software.
As for the Sony vs. the Cybook, the Sony wins hands down due to the newly released PDFLRF
program which makes PDFs a lot more readable on the Sony. Nothing like that exists for the Cybook at the moment. So I would go for the Sony based on PDFLRF
. I've used it and it's very very good.
The 2nd gen vizplex screen will not make PDF any better then the Sony's current gen screen. It's all due to the software. And since Cybook is being so closed about the Gen3 at the moment, I'd say they may be having issues getting it out to be ready in time.