First come first serve. It's only fair. I'd go in sets. if you do 10 every 3 months whatever. I don't see a problem with it. Random and favorites and bribes seem wrong to me. At least everyone gets a commission if you span them out long enough and you still get paid.
In my personal opinion, the most fair to me would be the first ten - on a first come, first serve basis. But for the artist's ease, if there are an overwhelming amount, picking the favorites would be best.
But I would choose whichever brought the most income in - money makes the world go round, and it'd only make sense to me to choose whichever would be most profitable. Especially if some of them were so profitable that it'd be almost impossible to say no to.