FYI IAD recently got a huge shipment of Audi A3's and A4's. Some are Quattro, some aren't. They all appear to be S-Line
The non-Quattro A3 appears to be YI, and the 2.0 Quattro A3 shows up on my receipt as X6.
Not surprisingly the Quattro is a much nicer ride and looks nicer. I didn't really like the non-Quattro version, although it still looks pretty good. They had no problem upgrading me to an A3 upon request for my last two rentals.