The 'gauge' of all of these is the same but the scale of the models depends upon what size prototype is being depicted - some are Narrow gauge equipment, some are 3' scale locomotives and I believe MTH chose 1:32 scale as the usual G gauge track is the proper width for American prototype equipment albeit too 'large' in other dimensions. Please feel free to correct me here to clarify this as I'm working from memory! Lol.
I display my USA Trains Hudson on 2 rail Gargraves as it appears somewhat prototypical for the American equipment. I cringe when I see a big steamer running on LGB type track!