Personally I quite like Pyhton 3, but the original comparison was flawed simply because with Fortran 77 you can just take your 30-40 years code recompile it with a new compiler and in 99% of cases will work.
While with Pyhton 2 to Python 3 there is usually a non trivial amount of work you need to put into migrating an old codebase.
Some answers are: it's faster, it runs on new OSes, it has better error messages.
Those then become the same answers to the OP's question about shifting from Python 2.x to 3.x.