We've typically used the Dakota digital units and have had good luck so far. They're pretty adjustable, can run 1 or 2 fans turning the second one on when programmed to a temp. Etc. Price friendly, their support on their products is excellent as is their reliability.
only drawback is they want them in the car as they are not water proof. I put then in a 5.00 project box and under the hood they go

DD 2800B Fan controller