There would have to be a pretty huge saving to offset the fuel cost in driving from either Munich or Frankfurt, surely?.... though you are right that the selection of cars in Germany is more interesting (they have the BMW M5, and a whole array of nice Jaguars on fleet). And if you do, you will almost certainly have to buy the vignette at the border, too.

Renting from the non airport locations in Zurich is fine, but they have far fewer cars on site, so you will likely get a more limited choice.

Someone asked if the Auris is "that bad"...... well, think of it as a hatchback Corolla (as that is what it is), and then decide whether you want that or a red blooded Alfa to drive around in. I rest my case!