definitely not the A4. Not only are they overpriced solely on their looks, but the 2.0T and numb steering will get you bored really quickly. If I had to go for one, it would be an Prestige w/S-Line. Premium is still a base model
If you want fun, definitely go with one of your 335 options (preferably the 09 due to updated everything and will still be in warranty. The 550 will be $$$ to maintain.