The Opus has the better mobile Adobe Digital Editions implementation for ePub, but the PocketBook is better for PDFs and supports many more ebook formats and also supports dictionary lookup. Overall, I would go for the PocketBook because of its hard cover and its richer feature set. Note that PocketBook recently bought Netronix (
PocketBook and Netronix to merge as PocketBook Global), so they are now the "third biggest manufacturer of E-Ink readers in the world" and actually make the hardware for the Opus.