That's a bit like asking which is better, a flapjack or a car?Masters degrees and CIMA are different things with different aims and take different amounts of time to complete.It would also be useful if you specified what subject the Masters would be in. It's not as if they are all the same.That said, you presumably already have a degree and I would always rate professional qualifications over (another) degree. The degree fades rapidly in usefulness after graduation whilst you will always have, be credited for and be able to fall back on your professional qualification.