My gut feeling is if Class AB I would want a small amount of quiescent current, enough that the transistors were biased on but just. No need for current flow to be any higher than necessary to get the transistors biased on.

If Class A, I would want the quiescent current to be biased at the halfway point, but that's the tricky part. The midpoint would be set not only by the current capacity of the output devices but also by the voltage rails oon the power supply. Which ever comes first is the limit, and the halfway point should be set by the limit.