Visa Therm and Ebo Jagger have both performed well for me. I think the key is using multiple heaters in a system. For example: if you need 500 watts to heat your system I think two 250 watt heaters is a safer way to go....if one fails the other one will keep the tank from getting dangerously cold. On the other hand if one sticks in the on position it probably wont fry your livestock. Just better than one failure point.
Likewise, if you plan on using a Ranco controller its still a good idea to use multiple heaters in case one fails the other will still keep your system from chilling to dangerously low temps. Prior to installing the heaters run them in a bucket of water for a day or two to set the internal thermostat at about 83 degrees "or your personal max temp." in case your Ranco were to fail in the on position the internal heater switches would turn them off "at your preset max temp.". This only leaves the Ranco not turning on as the only failure point. However, I have found the Ranco controllers to be extremely reliable.
Good luck
