The following comments are totally subjective and are backed up by absolutely nothing scientific, except my own observations.
I've owned knives in both of these steels. I got rid of the BG-42 knife pretty darn quick -- after like two or three days. The VG-10 was my EDC until I got something in CPM440V; now it's occasionally left-hand carry, occasionally primary carry.
I dulled the BG-42 knife, in medium use (cutting sandwiches, opening mail, slicing a cardboard box or two up), significantly more than I've dulled the VG-10 knife, in harder use (whittling a broomstick into foot-long lengths, slicing a cardboard box or fifty up, and of course opening mail) in the months since I've gotten it.
I've been told that BG-42's edge goes down fairly quickly after the first few uses and then holds the resulting edge for a long, long time. I'm sure that it does, and I'm sure that it works well for ninety five percent of what you'd want to do with a knife; however, I'm picky. I don't carry a knife that won't shave; I /usually/, since I like a polished edge for push-cutting, won't carry a knife that won't pop hair.
Just my opinion, just my observations. I'd love to hear if someone has another opinion. Oh, and regarding rust; haven't had any on my VG-10, despite wearing it IWB in 95+ degree weather, every day. The BG-42, I didn't have long enough to find out, but I think I've only heard of it rusting /once/.