I use the Tunze system right now, probably the most expensive one but it has been flawless since setup.
Precise water level, the optical sensor really can tell between waves and the actual water level. Very easy to setup.
I have a Tunze Osmolator. It's expensive but I managed to get one used. It has a number of features not available on cheaper systems such as dual sensors (both mechanical float and electronic) and an automatic pump cut-off so your entire top-up reservoir doesn't get pumped into the tank. These are important since they provide multiple failsafe layers. Many aquarium systems are been destroyed by top-offs gone awry so the more safety features an ATO has the better.