I spent a lot of time comparing the Audi A6 AWD, The BMW 525xi, the Infiniti M35 AWD and the Lexus GS 350. With the new 303 HP engine and the variable all wheel drive, the 5th generation navigation system and Lexus luxury I finally chose the GS 350. It is a wonderful car. It is well designed and an absolute pleasure to drive. I don't want to get out of it. If you haven't driven one and are considering any of the cars I mentioned, you should take it for a spin. I liked the M35, but with the GS 350 also coming in as the lowest "True Cost to Own" it is the right choice.
Interior, navigation system, bluetooth, and smooth six speed transmission it is hard to pick best features. But if I had to choose I think the best feature is the AWD combined with the smooth transmission.
18 inch wheels as standard would be an improvement. So would room for the manual (others have said this as well). Make sure you add a clear bra. Also would like to see navigation system include DVD capability and a holder for my iPod, a dealer installed accessory, but without holder).