Python 3.0 was released in 2008 and it has seen over seven years of stable releases including version 3.3 in 2012, 3.4 in 2014, 3.5 in 2015, and 3.6 in 2016. Python 2.x however will see no major releases. Python 3.x is the one that is under active improvement and development. For detailed information regarding the differences between the two you make look at the Python wiki. Furthermore, python 2.x will not be maintained past 2020.