Any place that requires me to buy a hat, scarf and gloves upon arrival has a tough chance of becoming a favorite but Berlin plowed through my cold-weather prejudice and left me smitten.
My favorite day in Berlin was when Gianluca (an Italian from my hostel) and I rented bikes and did a self-guided street art tour. I'm usually a bit wary of bicycling in the city (face planting on South Huntington Ave in Boston and having to be rushed to the hospital in a stretcher will do that to you) but it was fantastic and definitely the best way to get around Berlin.
The Jewish Museum proved to be the best historical museum I've ever visited. Certain sections of the actual building were designed to conjure up physical sensations within the visitor as they walk through (feeling sick, feeling alone) that symbolize the past, present and future of Jewish-German co-existence. It was tremendously effective.
LASTLY: before arriving, I figured the food in Berlin wouldn't be anything of note (bratwurst or whatever) but oh man, was I wrong. The food selection was epic. After a month of pizza and pasta in Naples, I was psyched about all the delicious ethnic food in Berlin (particularly Thai in Kreuzberg) and the doner kebabs were UNREAL. I barely consider kebabs to be serious food, just something you eat post-party at 3 AM but there's something about the bread they use that just takes it to a whole other level.
In conclusion, German's excel at doner kebabs as well as engineering. I don't even have a photo of a kebab but I just needed to share that with the internet.