dcvyn, thanks but I really don't want to buy two guns.
Since I'm looking at the same gun (just in two differnt calibers), the handling and wearing comfort will be basically the same. I guess the following are the factors to consider.
1) Capacity (9mm wins here)
2) Recoil (again 9mm wins here).
2b) Accuracy (depends on personal ability)
3) Effectiveness (.40 wins here, but the gap is a lot smaller than it used to be)
4) Cost of ammo (push with a slight edge to the 9mm)
5) Avaliable of ammo (push with slight edge to the .40)
#5 is mainly a concern for practice ammo.