The DC pump, you get a much more precise control and easy adjustment, it is also stronger so the skimmer is rated slightly higher. DC has the advantage that by slowing or speeding up the pump your water and airflow ratio stays relatively constant, with AC and an air adjustment as you decrease air flow you increase water flow. It is true in general that DC pumps don't last as long, our engineering target is a 5 year life for a DC pump and a 10 year life for an AC pump. With good care an AC pump can last nearly indefinitely with just impeller replacements as they wear, they lack any electronics. In DC pumps, the electronics wear out, you also have a controller and power supply that can be water damaged. DC pumps can be made to last but it requires heavy duty components (capacitors are the main weak point, the thin film type have a 7-8 year life span) that are very expensive and difficult to miniaturize (a tantalum ceramic capacitor can last 40+ years but they cost substantially more and are much larger and that is just one component, the others won't tend to last as long unless a comparable increase in quality and cost is made for every component). The Stream 3 is built to be a forever DC pump but this is reflected in the price and bulk. Bottom line, I would expect the DC pump to last at least 5 years, the pump can be replaced for about a 1/3rd of what the whole skimmer costs and in 5 years, there is likely to be something better or you have a different tank. FWIW, on my last tank build I went with the 9012DC and I am liking it so far even though I have just water, rock and sand to look at.
