No ebook reader is better than the Kindle. Its cheaper than the other alternatives like Sony and Barnes & Noble's Nook.
Kindle supports pdf documents it has large collection of books to download, light weight, amazing battery life, supports 3G and slimmer than Nook.
with Nook you cant access their store if you're living outside US though it has got a colored interface and supports multimedia playback.
So better go for Kindle. It comes with 6" & 9.7" screen size.