IME, LH is the best and SQ is (by far) the worst. The others I have travelled (AC, US, NZ, LX, NH, TG, OZ, BM) on were all basically nothing special for *A. Not coutning UA because that is my program, however, I could just guess that they would be in the middle.

SQ rates worst because of the before mentioned application of their own rules down to removing priority bag tags on luggage to those who would connect from a premium cabin flight to a Y cabin flight (as on Circle or RTW fares). Simply pitiful.