Python 3 was to some extent a reaction to the constant breakage that people were complaining about at the time. It was decreed that backwards incompatible stuff

Python 3 was to some extent a reaction to the constant breakage that people were complaining about at the time. It was decreed that backwards incompatible stuff would go into 3 and 2 would remain relatively static. Eventually it was announced that 2 would remain entirely static. That created an odd situation where the version that people were expected to transition from became a much better place to do new development in that it was a stable target. Heck, in a sense it is still better to target Python 2.7 for new development as the people running the reference implementation (cpython) have promised to stop changing things as a matter of policy. Your 2.7 based app could run basically forever with no changes. So you are dammed if you do and dammed if you don't. There is no definite answer here.