I think most of my ancestors on my dad's side were from Mecklenburg-Vorpommern, so I gave it a pity vote. However, my favorite would be a tie between Baden-Württemberg (mostly for Heidelberg) and Bavaria.
Ironically my ethic German ancestry is from outside of what's now Germany, both of my parents are about 1/4 German descent, on my Dad's side the German ancestry's from Alsace (now part of France) (off subject but Alsace is great, it's tied with Normandy as my favorite region in France) and on my Mom's side from Silesia (now part of Poland, and on this side it was a mixed German-Polish family).
I've already driven past Heidelberg but I've never been in it (but I saw the castle from a distance), but Baden-Wurttemberg seems nice, if I had seen more of it it would probably be my second favorite state. But yeah the best is Bavaria. The other state I've really been to in Germany is North Rhine Westphalia, which I quite liked as well but it didn't have the charm that Bavaria has.