If i was on a budget strictly with co2 tanks I would get the 20 oz becuase a 12 oz just wont cut it yould shoot one bag of paint, and then have to go for a refill, go with the 20, if money is not an issue defintly go with an air , they sell them for under 100, 47/3000 and 72/3000 which are as heavy as co2 tanks but are way worth the money.