I have had very few problems renting from non-airport facilities with Avis, Hertz and Budget. All the employees seem equally surly whether at the airport or in the neighborhood.

That being said, there are times when having to wait to get the car is more than mitigated by the savings.

For instance, next month I am flying to Seattle. I can rent a car for a week at Avis for about $350 as the airport fees are more than the rental itself.

Or, I can take the light rail into downtown Seattle (a 35 minute ride) and pick up a similar car at the Avis location in DT Seattle for $178 including all taxes and fees.

Even if the whole thing took me an extra hour, it is worth saving $172.

Edit: I was also reminded that you can pick up at an non-airport location and drop it off at the airport with no additional fees, which is exactly what I am doing in Seattle.