Another option to consider is flying to Germany's capital, Frankfurt, on LH in J (there's a non-stop from SAN). LH's J product is comparable (if not better) than UA's from my experience. You can then take a quick train ride to Berlin, Germany's population centre, of course after freshening up in the LH lounge on arrival in FRA. You might be able to get UA to even include the train portion since LH can ticket the German train portions!
I personally would not be caught dead in the Berlin airport. It's a real disaster zone in terms of facilities and everything else a real eye sore in the sea of German efficiency and quality. Here's to hoping that the new Berlin airport opens soon so that one day we can seriously call Berlin the capital of Germany!
Safe Travels,
James