I vote for A/C. Two reasons are:
1. Defogging the inside of the windows. I hate having to do that with a squeegee while driving.
2. Resale value. You may have to sell the car someday, God forbid! and that will be a good selling point.

Of course, if it helps get you some action with the ladies, all other reasons become unimportant.

I vote for Vintage Air. Jack Chisenhall is a hot rodder at heart.

R.