It's 2019, there is really no reason to use 2.x
Except 2.x is a better language, and 3.x broke backwards compatibility for no good reason. If a platform forces me to do a migration, it will be to a platform that respects backwards compatibility, not to the "newer" version.
How is 2.x a better language? Any specific examples? That is a pretty broad generalization and not really supported by a lot of the python community, except maybe the very vocal minority. I can see some things in 3.x that were done to be more consistent, example would be the print statement that uses () instead of space. Yes, it did break backward compatibility. I guess the question would be how much of a problem did this change actually make for you? A lot of people complain about things that in reality had no/minimal impact to them. Was there something that caused headaches for your migration, or are you just talking about backwards compatibility in general?
"In my opinion, Richard Stallman wouldn't recognise terrorism if it came up and bit him on his Internet." -- Ross M. Greenberg