I prefer Python 3 because Python 2 is going to be officially unsupported in 2020. Not only that a lot of new libraries and modules are going to be only in Python 3. Python 3 is also a tiny bit more syntax that Python 2 but its really good and I and a lot of the community felt it needed it. If you want books I'm not too sure or documents, but a Youtube Channel called Sentdex you can find his channel here he is really popular in the Python Community and check his Python 3 Tutorial here. That's pretty much it! You can check my GitHub, I post python projects that I think are cool I am looking for feedback so check my Steemit and Github. Thanks!