All mechanical and biological filters product nitrates. That is what they are designed to do. If you are shooting for zero nitrates, you need to do many water changes or go with the Berlin method - 1 1/2 lbs of live rock per gallon of water and a deep sand bed 5-6".
Elevated nitrates in a fish only tank isn't the end of the world - as long as you do regularly scheduled water changes.
All that being said, I am partial to wet/dry filters, expecially if your tank is drilled. They water movement is greater and they are the most efficient of all the external filters.