Of the two iterations (again 40.5mm and now 39mm), on the bracelet
link or the rubber, I prefer the 39mm as the shorter lug-to-lug looks better on
link my wrist. That said, they don't feel all that different, it's more in the visual presence. Conversely,
link if you're a NATO-or-nothing type, I think the 40.5mm is better balanced to suit a NATO, thanks to the wider case.
link