Personally I have a new Galaxy nexus with a 4.65" screen that is just perfect for me. I don't think I could go much bigger and still get it in my pocket. I have not tried to read on it yet mostly because I've just have not had the time to read since I've gotten it
But one of the reasons I went with this phone is that I can use it as a small tablet and reader when needed. I've had a tablet and found that I really did not use it that much when my ThinkPad x61 is such a nice to carry around laptop. But there were a few things I did find use full to do on it but did not really want another device to haul around. So I started looking at the bigger phones and ended up with the Galaxy Nexus I think it is the right mix between functionality and size.