I got the bigger GOSM.... for the money you can't beat it. I had about 2/3's of a propane tank and ran it for 8 to 9 hours. I took the tank off the smoker the next day, put it on my grill and still managed to cook hamburgers and hotdogs. Plus I used the tank to season my GOSM.
It might cost more on fuel. I don't have a comparison. Filling a tank here is only 11.50 with tax ... a small price to pay for good food.
I enjoy the fact that I can put a whole slab of ribs on each shelf. I cooked a 6.5 lb boston butt and 2 slabs of ribs...plus the extra cuttings and I had room left over. The extra space lets me make extra meat for lunches for the whole week