But if I were just buying a single watch?
A Rolex Submariner is a solid choice, classic design and it will appreciate. Decent heirloom piece. Daytona, especially ice blue, would be an aspirational watch that would be a highlight of any watch collection.
Breitling Chronomat B01 42 is an awesome chronograph that would be awesome to have.
Omega’s Seamaster line has some killer designs.
I like Tudor’s as well. Their new Alingi racing collab on the Pelagos FXD is a really attractive casual watch.