Originally Posted by
ThermionicScott
Go straight for the 50/34 and save the 53/39 on a shelf in case in want it again when you're in better shape.
This is the right answer. 53/39's used to be the standard for a long time, but if you are doing any considerable climbing there is a reason 50/34 is the new standard. Keep your existing cassette if it isn't worn out.