When I think of airport hotels two thoughts come to mind.

1. Tired, overused, worn out. Not always true but often true.
2. Not within walking distance usually to anywhere so often you are stuck eating there and often the food is lousy.

I happen to like the Helmhaus hotel in the old town, primarly for it's location. Nothing over the top but 4 stars nevertheless.

I'm no expert, but I thoroughly enjoyed my time in Zurich, and it seems to me that if you decide to spend your extra days in Zurich (and I don't think you have a bad choice here -- Zurich, Basel, and Lucerne all have wonderful features), it would be to your advantage to maximize your opportunities to take advantage of what Zurich offers by staying IN the city rather than staying near the airport, even though the airport is only a short train ride away. Just my opinion....