Getting start with CI 2.x OR 3.x

I'm php programmer and using pure php for few years. I'm not professional php programmer. Few years ago i started to learn php by myself.

I had experience in Wordpress developing/customisation and 4 years working as php developer in companies.

I spend my time couple of month to looking for a framework to learn such as ( zend, laraval, CI, Django(python), flask(python) ) . last times mean 4 months ago i was learning CI and i done the tutorial (NEWS). I'm tired to searching for all web frameworks and my decision is learning CI.

Now when i check the CI website i saw CI has new version which is 3.x .

Which version is the best choice to start for me.