Over my time buying and selling Lego, what has come and gone the most has been the minifigs. Sets may bring in the most money, and work nicely in a profit margin, but the minifigs are my bread and butter. And of these, Star Wars figures are the most popular. There is a cycle with these figures. When a new set comes out with new figures, the price of them - regardless if they are Jedi, clones or whatever - the price sparks as people want to collect the fig but not always the set that it came in. This is a nice bubble to sell in, but it quickly dissipates as the set is out for a month, a year. Then, the set becomes retired and the price slowly rises again. The key is to sell minifigs either at the first bubble stage, or hold figures until they become valuable. The best time to invest is about a year into set release, when the market is saturated and the price is low. For example, the Clone Battle Packs were very cheap around a year after they were released (2006). From there, holding around 100 figs proved very profitable. Its not worth it to buy just ten or twenty figures. The difference between selling minifigures and sets is quantity. Being the only seller with a quantity of over 100 is a good reason to charge more than everyone else.
Hope this helps.
Hope this helps.