How much do you want to spend?
I have a Tekonsha Prodigy P3 that works well for me, but seemed a bit fiddly to get set up. (I'm picky though, and tend to switch it in and out of boost mode depending on where I'm driving.)
controller seems to be an excellent unit, it's much more expensive and requires more intrusive installation (it requires a sensor in the hydraulic part of your vehicle's braking system) but the payback for that is that it tailors your trailer braking to the actual pressure in the tow vehicle brake system.
The other expensive controller that has people talking is the DirecLink
controller for OBD-II vehicles that has some control algorithm that calculates braking for the trailer based on the data being passed around the tow vehicles data bus.
I have no personal experience with either of the 2 higher-tech ones I mentioned, but for myself I'd look at the Maxbrake one if I wanted to spend another $300ish on brake controllers.