Berlin is one of the few german cities where public transport is done right. In cologne, where I lived, there are a lot of stops, but the inferstructure is just realy bad. They managed that trains get stuck in traffic too sometimes. And for some reason they trains only arrive in a 10-30min time window. So if you want to follow one line it's relatively fine, but if you have to change trains you have to be lucky. In the city center still faster than driving though.