Frank, in asking whether to use MTH 42's or Ross 72's, you're comparing apples to oranges. The more pertinent question might be, do you need (or want) 72"D switches or 42"D switches on your layout?
If 42's are called for, MTH is your only choice in standard gauge. For the 72's, you have options. I have 56 switches on my standard gauge layout, and about half of them, mostly on the main lines, are the Ross 72's. I still have some MTH 72's on areas less travelled like yards; and I have several MTH 42's in the tighter areas where I need 42 curves and switches.
All of these switches, by the way, work very well, I can't remember when I last had a switch-caused derailment, and I enjoy having the variety. Each type meets a different need.
david