Pretty sure the resolving power of what they speak of is the ability to resolve in arc seconds
(angular resolution). That is.... ".56" can resolve objects .56 arc seconds apart or size.
Obviously smaller resolution is better although not always. In general atmospheric conditions and light pollution will scintillate the air so (and illuminate the air with scattered light on dust particles) much so that resolving below around 2 arc seconds is probably the limit of
Atmospheric seeing for most.
What's best...they are all good.