Besides speed, I never seen any good argument that would make me start a new project on 2.7, rather than the latest v3 release. I get that there was a series of data science libraries that wasn't supported initially, but seems to have been solved at this point. So I really do see why people continue to hate Python 3.
I'm not going to argue that the transition couldn't have been handled more smoothly, the period of broken libraries and terrible performance was a little too long.