I’m far from a one watch person, but the 2531 is in my all time favourite watch list, and in my watch box.
If I was ever able to do one watch it would have to be an iconic watch, and over 100m WR - the SMP fits that bill.
But so would:
A Seadweller
A Sub
An Aquanaut
A Nautilus
Plus many many more
The 2531 is by far the better value prospect, despite the possible future value growth/retention of any of the others. I wouldn’t be without mine, in fact I had three at one stage.