I saw a great video about this topic by goodereader on youtube but I'll link it at the end of this post but I wanted to give my opinion first.
In 2007, I bought a Sony Reader PRS-505/SC (silver color) updated with the customizer firmware from 2010. I bought the book light (Great Point Light 3x2032 battery sucker) which worked but was bad on glare and hard to read at night. I've been using this combo for 7 years now just fine.
After seeing a friends Kindle in 2012'ish I saw how much better the contrast was and decided I wanted an upgrade...which I got this year (2014) and love my new PaperWhite 2. The clear day reading is perfect and the fact that it has a in built frontlight which is super clear at night makes it very easy to read. The only thing that would get me to upgrade in the future would be color and faster refresh times or some other technology like oled or something else which acts similar to epaper's readability and battery life.
Here's the video which sums up pretty much everything everybody in this thread has said plus more.
https://www.youtube.com/watch?v=WDxv_9y2LAo