In general, I feel that AC in-flight service is fairly consistently 'blah'. It's tough to quantify, but when I fly SQ, as an example, even in economy class, I know every flight attendant will smile, refer to me as sir or Mr. "JBB" and they'll consistently use please and thank you for every interaction. In short, they never make me feel as if I am imposing on them. I would say the same applies to NH, where the flight attendants bow to the passengers before taking their jumpseats every single time and OZ.

It's been a while since I flew LH, but one thing that stands out in my mind is how clean and well-presented the flight attendants were. Crisp, ironed shirts, clean uniforms etc.

Compare that to AC, where I've seen flight attendants bark out orders and not say please and thank you on a fairly regular basis. Even in international J-class, I often hear "Dinner?", "Trays out!", instead of softer, higher-end language such as "What may I offer you for dinner tonight sir?"

I concur though, that the best service I receive on AC is from the SD's and a good one can make the difference between a high-quality flight and a 'blah' flight.