Python 2 or 3?

Hello im a decent programmer in java but im looking to learn the syntax of python.

I have been given a book, but it is in python 2, and it tells you very clearly that you should not use python 3 when doing the exercises.

So my questions are as follows:
Should i learn Python 2 or 3?
What are the advantages?
Can you recommend any books or documents to read?

Thank you in advance.