October 4 will be the first anniversary of the purchase of my A5, so I have to decide by then. I have a great independent mechanic who I trust more than my Audi dealer. He's much cheaper too (obviously). However, my concern is that if there is a serious problem with the car down the road, Audi might try to deny warranty coverage because it was not serviced at an authorized dealership.

What do you guys think?

 

There are a few of threads about it already.
Anyway, even though you could probably save a couple of hundreds, having the argument with the dealer about some warranty item which they would claim was caused by unauthorized mechanic could be worth a lot more. In addition, dealer would provide a loaner car so you don't have to wait while service is being done.
I bought Audi Care with my car purchase.