If your intention is to primarily read library books then go with the Sony. Hands down. You can actually borrow the books on the device itself which is a wonderful feature. Browsing can be a bit awkward but downloading a book that has just been made available to you after being on a waitlist is an awesome feature.
People complain about everything. It's too sunny. It's too dark. It's too hot. It's too cold. Take what's best for you and go from there. I personally really really dislike Kobo's but I love Sony's. I have my reasons but I don't want to cloud your decision.
Do what works for you. There's a reason why there's 31 flavours of ice cream.
I'd go with the Sony because it's newer, because you can access the library directly on the device - no other reader today can do that, and I personally like the interface better than the Kobo. They're the same price of $80 at Best Buy Canada ending today so act soon!
The Sony's work right out of the box and are pretty much set, solid devices where you can happily read away. I have a massive hate of for a device that isn't solid from the get-go and has to constantly release new updates to fix things that should have worked properly in the first place. cough *Kobo* cough [<-- just my opinion but I'm not the only soul who feels that way!]