how do you decide what niches you will be promoting with your freebie sites please?

at the moment i am working with latina and twink type images but i am getting bored of seeing the same types of guy again and again so i was wanting to add some new stuff to my sites

how do you choose the niches of guys that you use images for on your freebie sites do you use personal taste or do you automatically know what will sell after a while?