If I'm buying fiction from an author I know and like, that I think I'd like to last for decades (and maybe leave to my children one day) I'll buy hardcover. That's maybe half of my fiction purchases.

For authors or books I'm unsure of, or just trashy stuff, I'll buy Kindle.

For technical books, I'll usually try to buy non-DRM PDF or eBook from the author, or failing that, a paperback.

I periodically (like, once a year or so) try to strip the DRM from my Kindle collection and back it up, but I basically assume that they could disappear at any time, so I don't trust them for anything I consider important.

I used to use an iPad2 for reading my Kindle books, but it's too slow to open the collection now (since I have a few hundred Kindle books). I'll likely get a Kindle reader of some sort one day, but for now I just read them on my phone most of the time.