Audi’s elegant midsize sedan, the A6, arrives in 2015 with new LED headlights, an improved MMI infotainment interface and a larger video screen. Four engines are available, all hooked to quattro all-wheel drive: 220-hp 2.0L TSFI; 240-hp, 428-lbs.-ft. 3.0L TDI V6; 310-hp supercharged 3.0L V6; and, only for the S6, a 420-hp, 406 lbs.-ft. 4.2L V8. While the S6 uses a seven-speed automatic, all others share an eight-speed.