I've always collected both scales.
I have over 400 12" figures, from various brands, and a rowing number from the smaller scale ( 25th Ann. and movie) I had hundreds of RAH figures at one time, and several dozen different vehicles.
The 12" scale has a LOT going for it, and the length and breadth of the offerings in that scale trump the 4" scale stuff by a huge margin.
IMO, if you are serious about collectibles, and serious about military themed figures, then the 12" scale stuff is the way to go.
But to be candid, I do not see the split in ranks that people talk about. The 12" on-line circles that I have frequented for over a decade and a bit have seldom, if ever discussed anything negative about the 4" scale. Aside from stating preferences, there's no slamming of the smaller scale stuff on the forums I know of.
There has been the reverse over the years however, collectors from the smaller scale lambasting the 12" stuff. I chalk it up to either immaturity or felling threatened in some way by the other stuff.