All four airports, but you get crosstown pay for each assignment from any of the three airports other than LAX and you can expense the parking cost at those airports. I don't know the crosstown pay amount for the LAX satellites, but it was around $93 for EWR/LGA and it's paid as per diem so not taxed.

You also have more time to get to the satellite airports when assigned a trip from short-call reserve. You'd have 2:30 to get to LAX for a SC assignment but there is no specified time for the satellites. It just has to be reasonable.