The New York 10 oz are much more common than the rounds with the Twin Towers, so you can get the 10 ozs for bullion value. Some of the rounds with the Twin Towers are low mintage, specifically those minted before 9-11, and have collector value. It looks like you got the Twin Towers round at bullion value from someone that was not aware of the collector value. There is a whole group of folks that collect the rounds according to type, and some are expensive. There are clubs and a websites that give values. I will see if I can find a link.