e.g., what value of solar flux value would be considered "good," ? Higher
better ?
A & K values ? Lower better ?
Why ?

For A and K values, the lower the number, the better. The values typically
vary with the strength of geomagnetic activity on the Sun's surface.

Generally, propagation conditions are best when the A index is 15 or lower,
and the K index is 3 or lower.

Besides causing auroral activity, high geomagnetic field conditions can
affect the electrons in the ionosphere, reducing the maximum usable
frequency (MUF).

Hope that helps?

Jackie