Really a tough question, as there are so many situations where a particular watch just isn't the right fit for the job. You really wouldn't want to take a Rolex Day/Date on a scuba trip, just as you wouldn't want to wear a big clunky dive watch with a Tuxedo. Really a lot depends on your profession, what you do in your leisure time.
Many years ago, before I got into watch collecting. I wore a gen Rolex 1680. It was my only watch. I wore it to work every day ( I was managing my families farming operation).When I dressed up, which wasn't very often, I cleaned it up and wore it with a suit or sport jacket. Wonderful watch, and under those circumstances, it was a good fit. Today, probably that one or my 16610 would be the one. However, today my choice would be my Rolex 16750 GMT, as it is a sport watch, has the GMT function which I need occasionally, and it could be worn with just about anything except formal attire.
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