I have a delta therm heater and it's brilliant :) It is adjustable with numbers, so you can set it to exactly the temp you want (eg - 78F) and continually turns itself on and off so you don't get cold water or the opposite - cooked fishies :)
Mine's only 25W for my 5 gallon though, you'd need the 50W :)
Whoops! Big mistake! Turns out that the so called "10-gallon tank" in my basement I was planning to use was really 40 gallons! That would be aound 200 watts for a heater right? But would they have different models of the Whisper 10 Power Filter?