This is a good article:
http://www.fitnessmagazine.com/workout/gear/sports-bras/
Based on it, I got the Moving Comfort Juno (but I'm a D cup). It's definitely great for keeping things in place -- way better than my old, standard Champion ones. One con is that it's a bit difficult to get on and off. Not a huge deal, but at the gym it can sometimes be awkward.