I have worked for both Lexus and Audi doing sales at the dealerships. Here are a few points to help you decide:
1. Either 2.0T or 3.2 QUATTRO A4's will be quicker than a Lexus IS250
2. The Audi is overall a much more solid and more fun to drive car (Quattro of course, if you dont get an Audi quattro, just go for the lexus, Audi FWD is a CVT Transmission and complete trash)
3. The Lexus NAV is MUCH Better, however the Audi Bluetooth is much more intuitive and easier to use
4. Audi has Dedicated iPod connections vs. Lexus AUX Jack
5. Audi will deal (especially if you come let me take care of you down in Newport Beach..haha)
6. Lexus styling is very sleek and luxurious (I like), Audi styling is awesome now that S-Line appearance is standard...however, I LOVE the Audi S-Line TITANIUM package!!!...LOVE IT!!!
7. Even the Lexus AWD does not compare AT ALL to the Audi Quattro....
so here is the quick and easy of it...
If you are a TRUE driver and enjoy driving a car for what its built for and are willing to buy the Quattro...go for the Audi HANDS DOWN...if you just want something squishy and comfortable to putt-putt around in, The lexus is great...Personally I own an IS250 and if I didnt work for lexus at the time I bought it, I'd have gone Audi 2.0T Quattro Manual Transmission in a heartbeat...