Ehiem. I always buy them and while no heater is perfect and immune to failure, they are great. The only downside, they are pretty large so make sure you have the room for it.
I would get a 75-watt Cobalt neotherm. That's what I used on my 15 gallon column tank and I loved it. Just bought a hundred watt for my 20 gallon Cube. Ehiems are good too. I would consider both of those Brands to be the best. I like the Neo therms because they are flat and skinny versus the other glass tube style. And they are solid plastic no glass.