I have recently used Ebo Jager 300 watt, Fluval M Series 300 watt, and a Fluval E Series 300 watt.
The most effective of the three is the Ebo Jager, it has a larger diameter tube for more surface area and has kept any tank I have at temperature (we frequently have temperature less than 65F, that's about 12 degree discrepancy). The heater is at least 12 years old, wasn't manufactured correctly, ie the scale is offset from actual by about 30 angular degrees. It is about 25" long further increasing the surface heating areas. I have accidentally run it dry multiple times, melting the plastic suction cups, but it still works. The biggest drawback on this heater is the size, on any shorter tank it has to be placed horizontally
The fluval Series M, is a good heater as well. It has a smaller diameter tube that is easy to hide in the aquarium. I like it, and would buy another if I needed.
The Fluval E series is a piece of poop in my opinion. I had it next to the intake for the largest Aquaclear filter and the heater would start to complain that it wasn't getting enough flow. I recently removed it from my 60 gallon because it couldn't maintain the temperature, going blue all the time. When I put the Ebo in rather than the E300 it again keeps the tank at temp. I don't believe you get 300 watts of power from them, additionally the instructions state they are only good for an 8 degree difference between ambient and tank temperatures.