I agree with tractorfix the 39 aluminum hoods (only 7 hundred or so made), the rest of the 39's ( as they are the first year made), the 42's on steel wheels and mags. I also would add the airport tugs, industrial and military tractors. Some also like the 1953 Jubilee as it was the first overhead valve engine. All of the Funks. Then some of the other modifications like the Road maintainer and an " earth mover" used in WW2 for makeing airports in the South Pacific Islands. ( I have only seen one).
It all boils down to how much and why you want something. I don't think anyone would get rich "collecting" Fords, but, but, it is a LOT of FUN. Have Fun, joe