40 because it has evolved hot enough from the factory to being a 10mm substitute at half the cost
A 10mm substitute? You are are referring to the lightly loaded (FBI Light) that most big ammo companies are selling right?
40 S&W no matter how hot can't be compared to Full house 10mm loads.
I did notice that you said
The 40 is perhaps the most versatile auto caliber for those that don't reload the 10mm.
but, what does that mean for those that do reload 10mm? Are you saying that if you reload the 10mm is more versatile? Don't the boutique ammo makers like Buffalo Bore, Underwood and Double Tap offer many of the full power loads in 10mm? So you really don't need to reload to experience the most versatile auto caliber do you?
LockedBreech, I did not mean to insult those that choose the 40. Not being much of a "Wordsmith" I was trying to point out that more people are paying attention to the overall costs and effectiveness of calibers they are considering.