How much $ do you want to spend? There are several ways to go, each with varying pros and cons.
1. Your typical all-in-one $40ish heater. They tend to be good for around a year. It seems that the thermostats stick or the seal degrades, allowing voltage to leak into the tank. Cheap upfront cost, but short lifespan.
2. Ranco controller, plugged into cheap heaters. Temp control is more reliable, but the heaters may begin to leak voltage. One typically sets the Ranco for the desired temp and the heater for just a little higher to act as a failsafe in case the Ranco gets stuck on. The cost is a bit higher than 1.
3. Ranco controller, plugged into a titanium heating element. Excellent option. One loses the "extra" thermostat, but a Ranco is very reliable. It costs a little more upfront, but it will become the less expensive option after 2-3 years.
4. Full controller (Apex, Reefkeeper, Reef Angel, etc.). This is the most expensive option upfront, but can be a very worthwhile investment depending upon your desire to control everything on your tank through a single piece of technology. You can use interfaces on your phone, tablet, or computer to program it, as well as access the controller remotely from anywhere in the world.
I think the best value in my list is number 3, but the most powerful option is number 4. Just remember that it is better to have 2 or more smaller heaters instead of a single, larger one. That results in a slower temperature change in case a heater fails, either off or on, because it only affects a small portion of the wattage needed to maintain tank temperature, and there is still a portion that is functioning properly.
