Is the .40 Browning more accurate than the 9? I would think so just because I've never seen the 9 be very accurate in any pistol except the Sig P210.
Most 9mms, like most handguns in general, are capable of more accuracy than most shooters are. The "accuracy" of a handgun is usually determined by things like sights, trigger, etc. and how the shooter uses them, and less by the actual inherant accuracy of the weapon itself. There are plenty of 9mms capable of shooting tiny little groups when shot from a Ransom Rest, but I promise you the groups will be much bigger when I shoot them.