What prime would that be?
If its a Nikkor, any 85mm 1.4, from the AIS to the current crop. If Canon, the 85mm 1.2 MKII, because the DOF is to die for, well, for me it is! I think the 85mm would cover sufficient areas in photography, especially, if you make it! The rest depends, on whatever I feel, or shot that day. I like primes, and here is my list when I strike it rich in the stock market, 30 years from today! Zeiss, 35mm 1.4, Zeiss Distagon 21mm f/2.8, ahh heck all primes all day 24/7 from Leica to infinity the sharper the better.