The 442/642 gets my vote, as well. I've carried one as a backup for several years. Currently it rides in my left front pants pocket in a Nemesis holster. I've also carried it on my ankle (at that time I was carrying a Glock 27 in the left pocket...current department only allows one backup).
The 340PD and M&P340 are nice enough guns, and the weight difference is nothing to scoff at, but they're over twice the price of a $350-$400 -42 and are even less pleasant to shoot.
"Logic is rarely the engine that propels a police department forward."
-David Simon in "Homicide"