I voted Sony. I have no use for nook wi-fi, I love how compact and light the PRS 350 is (especially compared to the old nook) and I plan to buy my books from whoever has them noticeably cheaper. Also, got mine from borders for $110 (USD) with no waiting. I am not a patient person.
I am not happy with B&N's proprietary drm, nor their interfaces: Books I load being segregated from books downloaded directly. The lack of updating a wishlist if they decide to change the price. Have to manually go in and delete the old version and then search up the new version, if its there at all. I also really dislike the look of the new nook.
I considered the kobo but the videos I saw made it look like it needs a few firmware fixes to be fully functional. Also, everyone in the Borders stores was completely clueless about when it would ship. (Some said "by father's day", others said end of July.)