Right now I'm happy with my iPhone 4. It fits in my shirt pocket with it snapped shut. I avoid any and all typing on it I can, and hate it when I shut it down and it asks for a bunch of passwords.
But I'm tired of carrying my iPad with me everywhere I go, just to have a library of books with me (and a bigger music library). I'm considering getting an iPhone 6 plus hoping that I can only carry one device, and still be comfortable reading. And buying more space for music (my music library is big). I have to carry glasses with me which I only use for reading, and I'm not sure how I would carry an iPhone 6+. If it's with my hands, I'm better off with an iPad, which I know I enjoy for reading books.