If I can only have 1 watch it'll need to work for casual, smart casual and most formal occasions and for everything else I'll just use my phone. My speedymoon:
If I could only keep one watch, it would be my faithful and beloved Seiko 6309-7049 automatic. It was my first “flying watch” and I purchased it new in 1987 at the NAS Whiting Field Navy Exchange while I was in U.S. Navy primary pilot training. I have flown hundreds of military missions and thousands of airline flight hours wearing it. 👍
Probably a Post Apocalyptic time piece should be a milspec self winder diver style with a long power reserve.
Vostock at the low end with the best you can afford for the upper end. Nothing gaudy so you don't get killed for your watch.