What is the best Kindle e-reader?

To keep the price low, Amazon has included ads on the Kindle E-reader. You can remove ads for an additional $10. If you don't though, they will appear as a screensaver (whenever you aren't reading they will display on the screen - this doesn't take power as the Paperwhite uses an E-ink display). They will also appear as a small banner on the bottom of the screen when browsing in the store.