I've had very good results using the Valley Odyssey controller when I was renting trailers. I once had to make a panic stop and I was blown away by how straight everything was after I came to a stop. Made a believer out of me.
Be advised that there are two types of brake controllers, time-delay and proportional. Go with the proportional type since it adapts to how hard you press on your brake pedal and adjusts its response accordingly.
Check this discussion of the two types:
Types of Brake Controllers - HowStuffWorks