NanaTravel, I agree with you. It is an excellent Caribbean Cave. However compared to caves in the mainland USA, it is a minor cave. Like most questions, this initial one posed can't be answered without knowing the originators interests and history.
I also agree that if you want to do Harrison's, take a taxi and beat the ship excursions there to avoid the crowds. If you hit it during the peak time (i.e. when the ship excursions arrive), there probably will be a wait.
Of course, why not do both, see Harrisons and snorkel. Beat the crowds by going early in the morning, then snorkel in the afternoon :-)