I think one of the best I use is the fluval e series. It has two computer chips on it and digital read out. Also low flow sensor and shut off it you leave it on and take it out of the water. Another thing the background has three colors on it.
Green = the right temp
Blue = water is below temp
Red = water is too hot
Flashing Red = Problem with heater
These heater stay very steady. I own 3 of them.