I'd watch only the sus2 (Asus2 = A, E, B) has the airy open sound. The add9 (Amadd9 = A, C, B) is extremely tense sounding. Now when the seventh is involved, the 9th tends to have a different effect on the chord. A major 9th is less "lush" sounding than a major 7th. Adding a ninth to a dominant 7th chord levels out the balance of the chord. The dominant 7th being on of the strongest of the chords, the ninth softens it up a bit. So when a dominant 7th seems to strong, add the ninth. Now by adding a 9th to the minor 7th chord will kick the chord up a notch. Of all the chords, the dominant 9th is by far the most common.