I'll be blunt: I think the burritos at Dolores are the best in Berlin. Okay, the place can get busy (both at K'Damm and Alex) and ordering / finding a place can be difficult and times a pain, especially as you have to order then find a place. Yes, the queues can be a problem with people deciding what they want once they get to the cash desk.
The burritos are the best in Berlin.
Go to the one at Bayreuther Str. The one near Alex gets too busy