Hi,
The wife and I dove with St.Croix Scuba. They are based in Christianstead right on Queen's street(right near the dock and multiple shops and most importantly the Brew pub(for afters). St Croix diving is spectacular and when we went there was no current or big waves. The operation was excellent and you don't have to worry about navigating back to the boat as they send a DM with each group. We were never crowded and Ed, the owner is just a gem. He has this huge dog in the shop who has really embraced the Carribean lifestyle. H e holds down the floor all day.
I heard that Ed bought an operation in Fredrickstead now, so it's possible to dive both sides of the island with just one operation. Also they offer some great hotel/diving/air packages. Big tip:Rent a car at the airport, the taxis will kill ya. Have a fantastic time!