I always prefer a 9mm over a .40. With modern hollowpoints, the effectiveness of the .40 has proven to be only slightly better than the 9mm; what matters far more is shot placement. And the slight increase in power doesn't make up for the lower capacity and slower follow-up shots. Add in the fact that 9mm ammo is considerably cheaper than .40, and it's no contest between the two. But that's just my opinion, the .40 is a good round that serves many people just fine.
0331: "Accuracy by volume."