The avant and sedan are mechanically the same. There's no difference in height between the avant and sedan other than body type, meaning the sedan does not have some sort of better or lower or wider suspension. The avant is a bit heavier but has a better weight distribution. Most enthusiasts think the avant is the better looking car. Most everyone else thinks it's just a wagon and doesn't get it. It does have more cargo space than a sedan. It is much more rare and will usually command a higher price. It's usually the one you end up wanting. You can't get an S4 Avant after 2008