I've found the best way to culture daphnia is through neglect. I set up a couple of tanks/tubs/buckets/whatever is handy that holds water, put the daphnia in, top it off with tank water from my water changes (NEVER fresh tap water, even if it's already dechlorinated). Sometimes I'll throw some food in (strained peas, flake fish food, greenwater, Jenn Macke's super daphnia food, whatever). Then I harvest what I need from whatever tub looks like it has the most.
I tried brine shrimp once. It was much more of a pain than it was worth when I was feeding hundreds of little mouths. I like the low-maintenance of daphnia.