I am looking at buying a used A6 and would like some feedback on which used A6 would you buy?And what is the better value? An 05 a6 certified with 47k miles or a 06 A6 with 36k miles not certified. Also looking at a base 07 A6 (just cold weather package) with only 25k miles. The first two are both are loaded with the same features and they are all in the same price range (just under 27K). What is the better way to go?

Thanks,