Which K frame would you use, given the choice?

73+ with spool mounts every time. Better engine mounting design, no chance of the engine shifting forward with an engine mount failure. Much less chance of an engine mount failure to begin with, unlike the biscuit style mounts that are notorious for failing. Better sway bar design routed through the K frame, increasing ground clearance and moving the sway bar mounting tabs further in, allowing for wider front tires and removing the interference issue you get with the 73+ calipers and the 67-72 sway bar design.

And the 67-72 K frames weren't made any better. I've seen examples of both styles that had great welding, and examples of both styles that had horrendous welding. It wasn't a production year thing, just plain old 70's mopar quality control.