For a very reasonable price, I would have to say the Emorer 400.
Mine has been running for over 5 yrs. with no problem. Just keep the filters changed, and turn the flow valve to the off position when feeding. Many have stated that they are a nitrate factory, but this is untrue in my experience. I have had a couple people that have had them, and they said this. They did not know about the valve that shuts off flow through the filters during feeding.
Of course your going to get high nitrates if you suck up all the food and it gets stuck on the filters. When I told them how to do the valve, all they could say was - "oops".