Both great cars.
I was deciding between them both as well. Went for the 'is' because of the handling, and the looks. I just like the look of the 335is better. The Audi's are a dime a dozen and for some reason, a base A5 looks just like the S5.
Also... funny story. I was in a parking lot getting a drink with some friends and a man came up and commented on my car. He had the S5 and said he test drove the 335is after and automatically regretted his decision to get the Audi.
(He then continued to tell me that he sold the S5 and just placed an order for an M3.