I'm not voting because I'm not sure if you want to read more or use apps more and the vote really depends heavily on that.
I have a Kindle that I use when I want to read and an iPad I use for internet browsing, apps, everything else. The Kindle (the one I have, I haven't seen the new one) is not backlit and is better for extended reading periods. When I read, I read for hours on end, sometimes an entire day. I spend a lot of time on a backlit computer and wanted something that would strain my eyes less when I read. The Kindle is good for that. I feel like I am reading a book, not a computer screen. It doesn't give me a headache even after eight hours of reading. It's lightweight and easy to hold and use.
The iPad isn't as good for reading because it's backlit, but you CAN read on it if you can only get one device. You can't really role reverse though. If you get the Kindle, it's good for reading and that's it. The iPad is what I use pretty much every day for web browsing, checking the news, buying things online, checking my email, etc. It's attached to my hip almost as much as my phone is. It comes with me to appointments, work, and pretty much anywhere else I go. My Kindle? Not so much.
The downside to the iPad is the price, but in my opinion it is well worth what I paid for it. At one point I was using it as a day planner as well. I use Franklin Covey day planners, so it was saving me about $150/yr on planning stuff by using it that way alone. I ended up going back to the paper planner because actually writing things down seems to help me remember, but otherwise it works GREAT for planning.
You can also get note taking apps for iPad. If you're in school or have meetings at work you need to take notes for, you can type them or write them all on the iPad and never have to carry another piece of paper again. I use this for all my work meetings.
I'd give up my Kindle if I was forced to, but you'd have to pry my iPad out of my hands.
If you're JUST going to read on it, however, get the Kindle. Your eyes will thank you.