I've used a Paperwhite, but for most of my reading I'm switching to an iPad Retina mini. The battery life is suitable, the screen is gorgeous (326 PPI vs 212: more than double the number of pixels per glyph) and I hope it will be easier to take notes (possibly even with voice dictation) and fire off emails and TODOs inspired by what I am reading. Most of all, though, I want fast PDF and Pocket/Instapaper in full color.

EDIT: I have not yet tried the Retina mini as a Paperwhite replacement except for an hour in the Apple Store. It's on the way. The in-store experience satisfied me sufficiently, but there is a chance I will come across a deal breaker.