Different opinion here. I find the Sony PRS to react much slower than the Cybook when turning a page, especially when it is graphics as with comics.
So, I would rather advise you to buy the Cybook - if the missing folder option wasn't such a pain in the butt till now!
Since you can't collect your comics into folders, you have a laaaarge list of pages in the library, each page as one file.
You may convert your files into one pdf, but pdf aren't the fastest on the Cybook either if they aren't optimized.
Still, the rather open format of the Cybook is THE major argument for me.
K-Thom