Car appreciation... the aesthetics, the engineering, etc

Most important is lack of rust, and evidence of proper maintenance.
Then I'd always go for a straight 6 over a 4 just because they are nice and smooth. Neither are what you would call fast.
But the 4 is probably a tough old beast, and almost certainly drinks less.
The 6 is less likely to come with nasty plastic seats.

Based solely upon interactions with middle managers of an independent German, (Ruhrgebiet), chemical company back in the '80s;
Get the 6, you don't want to be mistaken for a taxi driver.