Simple. NONE. Or ANY. Since there is some interest, I'll offer my two cents on this topic.
I have a regular Kindle. I love it. I've read this year more than any other of my life. I've read wonderful public domain books. I've been able to have titles for my daughter's education I could read from it before I came across a paper copy, or saved for the real book.
Like all of you who don't have a reader or Ipad yet, I did lots of research before getting mine. I did not want to mess this up. I needed to be sure I got the right thing. I ended up with the Kindle and not the 3G because my dh said I don't need 3G, and I don't know what that is, so it was fine with me. I preferred Kindle because I am an Amazon person. And now you have more choices... choosing is getting very hard.
You don't browse with a reader. I don't even buy the books from it. Yes, even the 0 dollar books you have to click buy. I do that from my computer, because the reader Kindle does not a good job of finding the free titles, and it's not very maneuverable to surf the Internet. Every time I lay my hands on it it's to read, charge, or load it with books from the PC that I did not get straight from Amazon, those go straight to it once I buy them with a click. The others you find here and there, you download them, save them, and connect the Kindle to your PC like you do with your camera, and instead of uploading pictures, you pour down the files in the Kindle folder.
But if you have more budget, the Kindle Fire is nice. Why? Because it's more like an Ipad but not as expensive, and it will enhance your homeschooling. You can find and identify birds, listen to their songs, listen to anything in Librivox, read from it too, read blogs, check email, and get applications or inexpensive programs for a diversity of subjects and interests. And if you can afford an Ipad, it's something you will use for your whole family's education, so no remorse. Ah, did I tell you guys that libraries now loan books for our readers and even Kindles themselves?
But please, don't call me traitor. I'm very fond of real books, I don't have many expenses but what I invest on books. I don't think books are threaten, but the market for them is shifting, and all of us who love books still have them, gift them, buy them, READ THEM :). Many titles are being rediscovered thanks to this new ability to read them with readers. Many of those nineteen century books, would be non accessible and hard to read on computers. I may be trying to justify the fact that I'm in the e-book world a bit and not just in the true book world. Anyway, that's just my incomplete opinion.