I used to fly between London and Berlin a lot, and absolutely loved Tegel then. LCY-TXL was a great route. From my apartment to sitting on the plane at LCY took 20 min; from my desk in Berlin to sitting on the plane at TXL took 40 min. Probably the best two airport experiences I've ever had.
LCY seems to have gone to the dogs recently too. I like the redevelopment they’ve done on airside, but it’s all so … full and unpleasant now.
Food options seem to have gone downhill now that the ok airside restaurant only does burgers. I’ve had delightful meals there in the past, making delays more than bearable.