Capturing multiple pieces is almost always better, The only exception might be if there's a specific piece that's better for you because it's size/color will get you closer to completing a mixed-color or monochrome trio.

Smalls are harder to get than mediums, and mediums are harder to get than larges, so this informs the value of the capture as well. You're likely to be looking for smalls to complete your trios, monochrome or mixed-color.

Look at each stack and imagine the pieces going out in an eruption in various directions, and check where they will land, to see what captures would result, if any. Remember to account for the movement of the cap itself when counting out where pieces will land.

The cap will always land in the space nearest to the erupting stack, and the pieces in the stack will move out from there. So the top piece will land exactly two spaces away from the stack, the second piece down will land exactly three spaces away from the stack, and so forth.

This is the time to consider whether a Power Play will enable you to capture some specific piece, or make a double capture that will make the sacrifice of the piece placed back on the board worth it. You can do it any time before you cause an eruption.

In the example above, a single large would be captured. If you had a medium of a color which was not advantageous, but you wanted that (light blue) medium, you could decide, before the eruption, to put your previously captured medium on the board where the light blue medium will land.

Then this eruption would capture you not just the large, but also the medium, of the same color. You would have effectively exchanged your less desirable-colored medium, for this color, which you presumably needed more (or at least it matches the large you just captured as well).