My stack for web developing includes Django/Python and Qt/C++ for non-web developing.
What is most comfortable OS for a developer with such a stack ?
Once you go linux, you'll never go back (though you might go crazy and move onto bsd).  Ubuntu is probably the easiest OS to start with, if only because of the truckloads of documentation, forum assistance, etc.  Good luck!
Which OS recommended for Programmers?