Good question.
It isn't until you play with LEDs that you start to see the differences.
Under playfield inserts use super brights. Generally cool white wedge and bayonet type. Under red inserts use red. Under green you can use either white or green. Blue is much the same. Flashers generally leave them or you can change them but not a big deal. Then also get the flex type bayonet for to inserts.

When in doubt start with cool white.