St Croix has better diving but St. John is more "multi-purpose". St John is closer to the British Virgin Islands if you want to do some island hoping. 70% of St John is a National Park and has GREAT hiking. It's really unfortunate that travel between the two islands is a real pain in the arse. St Croix is about 45 miles from St John and you have to take an airplane. St Croix has the distinction on one of the deepest shark attacks on record (if i remember correctly).. Oh Boy! Here is a breakdown on some St John dive sites: SCUBA DIVE VI | CaribbeanBoatTrips.com