Hi,
I've had a 442 for awhile and I've had zero rust issues with it. I don't baby it either, I carry it on rainy days, high humidity days, etc. It rides in a pocket with a cheap uncle mikes holster or a smartcarry. Every few months, I give it a coat of oil, but that is it.
For me, the one big advantage of the 442 is the sights were consideraly easier for me to aim and see with. I also like the black finish.
The finish has however picked up the surface look from the inside of the uncle mike's holster which is sort of a pattern.
Some 642's really turned me off because the stainless and allow looked completely different, but I've seen some recent photos of a 642 that shows the finish on the aluminum much closer to the stainless which look much better.
The sights would be my most important reason to go with the 442, but if I was in a serious water environment like on a coast near a beach, I'd go the 642 for the added corrosion protection.
Good luck,
Alan