Try to present the pros and cons of both.

Buck pros: Usually a bigger deer, self satisfaction for taking the harder of the two to harvest, chance for a nice trophy to mount.

Buck cons: As a rule, harder to harvest (tag can go unfulfilled).

Doe pros: As a rule easier to harvest, good eatin.

Doe con: No antlers to mount, normally a smaller animal (less meat).

These are just some, I'm sure there are more out there. Remember in life there are two tragedies; 1.) Not meeting your goals and 2.) Meeting your goals (then you have to set new ones).
Let your friend make up his own mind. After years of holding out for a buck, I started to take the occasional doe. I realized I liked hunting DEER, and getting a buck is special, but when I unwrap the freezer paper, the steaks and chops, taste just as good. To each his own.

Either way, good luck. I hope you both have a safe successful hunt.