I have always driven my personal (UK) car to the big countries of the mainland Europe.
I've driven over in a miniature Toyota - once, never again - my back and legs wouldn't let me repeat the journey, manual transmission, 1.0 lire petrol, no overtaking, all the way to Switzerland and back - no cruise control.
Same in a 1.3 petrol manual Corolla - again no cruise control, but I did have air conditioning, surprisingly nippy on mountain roads but the brakes got too hot too quickly. So, again, just the one trip.
For almost 10 years I drove over in the 2.2 litre manual diesel Honda Accord Executive. What a dream to drive. 5 speed, cruise control, arctic airconditioning, huge boot, excellent winter heater if a bit slow (typical of diesels, because they run much cooler than petrol the heater takes longer to heat up, but then excellent), and just simply a fabulous car to drive. Nippy (nobody would know it was a diesel), huge amount of grunt and the car just loved the mountains. First gear mountains near Chur and Seefeld in Tirol and the car just laughed and buckled down. Same going down, that big engine was a great engine brake.
That car finally gave up the ghost and for 3 years I've been driving a new model Honda 1.6 litre manual diesel Civic. With a 6 speed and all sorts of technical whizbangs it is a truly spectacular car to drive. Huge low speed grunt, happy to cruise at 180 kph which is where I like to be (between 160 and 180) in Germany, but perfectly happy at 120 to 130 elsewhere, a little more lively than the Accord on rough roads but with a much stiffer suspension, but not so happy as the Accord going down steep mountain roads - the smaller engine gives less engine braking so there is more load on the brakes, and the brakes are smaller.
So in addition to the simple question of manual vs automatic there is the question of fuel type and how many gears, and how big an engine.
Just by the way, with the Civic I get about 800 km per fillup (45 ltrs) in mixed driving, about 1200 km in the East of England, France, and Netherlands.
I'd never want an automatic in the mountains because it is not easy to use engine braking on the downhill, and there would be too much hunting uphill.
I don't get fatigued by driving until it has gone too long and I'm just plain tired. I've never used paddles, always a traditional gear stick. In the 1960s I used a 3-on-the-steering-wheel manual on a Chevrolet.