I have had the best luck with Finnex. I don't trust any of them however, I use them all in conjunction with a controller.
Yeah when I replace this next one Im just going to hook them both up to my heater controller so the internal thermostats don't have to turn on and off.. the controller I have actually has a relay inside to switch the heaters on and off so I trust it a lot more than the mechanical or electronic style heaters with builtin thermostats.