Some watches I only really like on their matching bracelets (RO, Nautilus). And while I think Rolex sport watches work best on their oyster bracelet, I don't mind them on a NATO now and again, but I would never put them on a leather strap.
Here are my favourite combos for 3 different black dialed sports watches:
Speedmaster on black alligator:
Luminors on mid brown distressed calf:
And I really liked Cleav's recent paring of the more dressy Radiomir with a darker brown alligator: