Clowns are perhaps the least picky eaters in the ocean!! Mine have eaten virtually every food I have thrown in there.....and even gone after my fingers a few times!! Those little orange sharks are eating machines.
As for what is best for them, mix it up. My fish never get fed the same thing in any 4 day period. The menu rotation consists of: Mysis, Formula One, Prime Reef, finely chopped clams, Squid, My custom slurry, cyclopeeze, and they even enjoy formula two!!
One or two constant sources of food will eventually lead to nutrient deficiencies so keeping it mixed up will help with that as well!