Hopper-ACF
I voted hopper.
I like the short 34-40 ft. ones for coal hauling but my all time favorite if the 55' ACF Centerflow Hopper that carries grain. Being that I lived in rural Arkansas at an early age I remember those car quite fondly and have 36 of them on my layout, albeit, not all SSW/Cotton Belt.
I like the BN ones because of the green paint scheme.
The ROCK ones are cool too, great name.
I have Athearn,Atlas,Intermountain and some others.
jai