I just bought a Kindle Fire HDX a few days ago. So now I have an old kindle, a paperwhite and an HDX. As far as reading a book, the paperwhite is the best. The HDX is good for reading too but not as good as the paperwhite. The paperwhite is only made for one thing and you can't beat it for regular reading. With the HDX, you can buy magazines that are exact replicas of the printed versions. There is a bit of a learning curve in figuring out how to magnify what you want to read but I am really liking that and I'm still figuring it out. The HDX has a terrible user manual and I'm just figuring things out on the fly. The HDX is basically a tablet and you can play games, music, go on the internet, etc. You can even stream from your Amazon and netflix accounts. I like having both the paperwhite and the Fire.
One thing that I like about the HDX more than the other type of kindle is the ability to read pdf files. Whenever I'm on a news or magazine site and there is a long article I want to read, downloading it and making a kindle file is my favorite way to read something like that. I have a hard time reading long articles on a regular computer screen. The easiest way to transfer files is with pdf files. You can get an adobe reader app with the HDX and the file is much easier to handle on the HDX. I haven't read The Plant yet and that is in pdf so I'm going to transfer that to the HDX and read that soon.