Well, I made the wiki page -
https://wiki.mobileread.com/wiki/Sony_vs_Cybook - in the hope that we could just point to that!
For me, the Sony's got a nice feel to it, the multiple-buttons are very nice, as is the clock (via modified firmware). The ePub support is useful and I don't miss Mobipocket as if needed, I could convert it but, if you think that a dictionary would be useful to you, then it's the Cybook that you should probably favour.
Bear in mind that in reality, they're both going to display the books on the same screen & neither will be a 'bad' choice...