First off, I prefer Ebo-Jager-Eheim heaters - I have some that are 20 years old. And some that are 10. And some that are 5. I hear good things about Aqueon.
I find most people vastly oversize their heaters - I rarely use anything bigger than a 150. (My 60g in the garage uses a 150w - it was fine until the temperature remained under 50 degrees (in the garage) for consecutive days - then I just threw another heater in it-we all keep spares, right?)
Tropical freshwater fish are used to temperature fluctations. When my clown loach tank hit 92 degrees I started floating ice in it until the heat wave passed. They didn't change their behavior at all - though my synodontis became much more active. In the winter, I let them get to 69 degrees before I add another heater.
The tanks in the house I set at 74 degrees - which means they are off all summer as my AC is set at 75 overnight and 80 during the day. In the winter, the tank heater only has to work to raise 12-14 degrees at most - so I again I use a 100-150w heater for any tank size. If the tank temp drops down to 70 over night a few times.... no biggie. And the bigger the tank, the less drop I get... so again... 100-150w.
I prefer to let my fish have some temperature fluctuations - most people are not comfortable with that - people strive to create ocean like conditions - same temp year round. I find the cooler temps in winter allow fish to live longer - 8-10 year old fish are common for me - and we are talking otocincluses and rainbows and the like, not big bruising cichlids.
Also, what wears out a heater is the constant on/off cycling it does. An oversize heater will click on and off more often than an undersized one - or as I prefer - a proper sized one. Its no different than your home AC unit. (also, use two small heaters instead of one big heater - can't cook your fish that way)
Lastly, as others have said, it depends on where your tank is, what fish you have, whether your tank is insulated (Styrofoam on back?), and what range of temperatures that area is exposed to during the day/night.
I hope this helps.