I have only occasionally used a small Tetra heater so I don't have much experience with different heaters, but I might be able to help anyway. If you don't already know, there are three main kinds of heaters. Preset heaters are permanently set at a temperature of about 78 degrees Fahrenheit. The other two types are adjustable, one just has a knob with a + and - sign and an indicator light to show when it's on. The second, most preferred kind lets you set the temperature to whatever you want. Also, I think the main guideline is either one, or two (look it up because I can't remember which is right) watts per gallon. I did do some looking and the EHEIM Jager heater looks really good.
Off topic here, just curious, is this your first tank? What fish do you plan to keep?
Hope this helped!