- The later B7 got the rear biased Torsen T3 centre differential which defaults to 40:60 (front:rear) and can send up to 80:20 or 0:100 when needed. I forgot the year when they did this, but it should be either 06 or 07.
- Better flywheel in the B7 if you're getting a stick.
- Newer ESP, which most people can care less about.
B6 and B7 are both great cars. Things to watch out for:
- Valve train noise and timing chain guide problem, oil consumption from worn or scorched cylinder walls, these problems. These problems might call for an engine replacement.
- The tiptronic is a ZF 6-speed. Because Audi claims that the ATF is good for life, rarely do people change the fluid. There's no such a thing as lifetime ATF. If you're getting a manual, worry about the flywheel.
- As these cars are getting older, pay extra attention to oil leak (especially from valve cover gaskets), HVAC, power window regulators, power steering rack/pump.
- Get a leak down or compression test done!