Python 2 or Python 3?
If you have a choice, use Python 3. Especially if you’re a new to Python, so you don’t need to unlearn some of the Python 2 misfeatures that Python 3 was designed to correct. Python 3 has better Unicode and strings management for example. Besides, why not learn the most up-to-date and more future-proof version? And also not that many Python 2 popular library which hasn’t been ported yet to Python 3. Check out Python 3 Wall of Superpowers, Python 3 Readiness and Can I Use Python 3? for the data.
If you stuck with Python 2 like because the library you (really) need still hasn’t been ported to Python 3 or you simply don’t need to port to Python 3, then just use plain Python 2. Just in case you want to migrate more easily to Python 3 in the future, use one of the bridge packages like 2to3, six, python-modernize, python-future.