I have both a Sony & Kindle. I bought a kindle in April and I have had a Sony since September I think. I like them both and probably will be keeping both. I thought I would part with one but I can't! I have never been too much in gadgets like my husband so having 2 readers is still less gadgets than he has!
I like Sony's size and looks much better and if there store had the level of ebooks and prices that I see at the kindle store it would probably be my only device. I constantly find bargains at kindle store. I recently for instance got the next 2 Daniel Silva books I wanted to read for 3.29. I have caught on that the kindle store has bargains you really have to search for and they prices will jump up after a couple weeks or so. Last month I got a Heinlein book and a historical fiction book I had been meaning to read for the bargain price of 35 cents! So its things like that why I keep the kindle. And I actually do prefer the page turn buttons on kindle. They are light to the touch which is great for me since I sometimes have problems with tendon strain. I just wish the device was as thin as the Sony. I also like the font they chose on the kindle. I find it easy to read with and I like the dictionary and also like that I have 6 fonts to choose from. There are times on the Sony that a book in medium I think is a bit to small but large is to big. I never experience these problems on the kindle. I really do hate the white color! But I have bought a decalgirl skin in a blue design and that helps.
For the SOny, along with looks I really like epub. I have bought a few titles from British ebook sellers that I can't get anywhere else. So thats been really cool. In general I think both epub and Sony's format looks better than the kindle format does. Less issues that I sometimes see with kindle books like gaps between words and such.