We have owned new 98 A4, 2.7l leaking oil mess, 2000 A4, used 150k sold after replacing timing belt, front strut parts and was having electric gremlins at the end. 2005 A4 used , the usual timing belt and electric stuff but my wife drove it when radiator blew a hose and toasted the engine
, 2006 A4 used, timing belt good car with minimal stuff. 2013 A4 current, new with 41k and warranty will run out next june, so far a nice one.
My advice stay away from a Audi that was built before 2010, anything newer and you are OK.