You pointed it out: a 4-speed is difficult to find, automatic you have more choice. I wanted a 4 speed and found one - with the circumstances that it was soon a project. I don't regret because I always wanted to have one. But from time to time, as I drove it before taking all apart I felt an automatic would be perhaps less stressful to drive sometime. With a 4-speed and a healthy motor it is difficult to cruise, with a idle at ca. 1.000 rpm (351C 4V) the car wanted always to be driven. You are in a permanent race modus
That's the charm on it - and don't forget the pedal forces and pedal ways which are needed to shift - it is not as on your everyday Volkswagen from 2015...
I think an automatic will be the better cruiser and the 4-speed the better racer. But you can do also both with them important to say. A 4-speed will be hanging more directly on the rear than an automatic which will react a bit more softer at the end.
It all depends on how your drivestyle is...
Driving automatic is not that difficult to learn. If you can drive with a hand-shifted car you can also drive an automatic in general.
In case of doubt better buy the better car - the original and the untouched the better - if that car has an automatic or a 4-speed is then secondary...