7 dive shops are listed at the following site,  take a look around and
see what appeals to you. The site also contains a dive site map, you
will notice that most are located on the north and some on the west
shores.  I would consider using 2 or 3 shops that are convenient to the
areas you wish to dive in rather than booking all your diving with just
one shop. We did some nice one hour dives on the north shore last week,
but the boat rides to the sites were often long since our hotel packaged
dives departed from Christiansted each morning.

http://www.diversevirgin.com

Frederiksted (west side of the island) is currently undergoing some
construction, I would stay at a resort/condo on the north shore
convenient to the Salt River/Cane Bay area or else choose a hotel in
Christiansted if you prefer to stay in town.  Having a kitchenette is a
nice option in either location, our hotel restaurant was only open from
8am to 5pm some days.

Diving was decent, better than what I have experienced in St. Thomas.
We saw turtles, nurse sharks, a couple of eagle rays, a couple of
morays, and an assortment of the usual caribbean reef fish.  Reportedly,
there is a chance to see bull sharks cruising the drop off at "The Wall"
at Cane Bay if you don't mind getting up at dawn - we didn't try.  We
spotted dolphins from the boat several times, but they were never around
during a dive. Several sites can be done from shore - including "The
Wall". Viz was 50 to 70 ft. at most of the sites we did and you should
have no problem staying within your stated depths.  Surface conditions
were very bouncy for us (as was the plane ride home with Hurricane
Dennis to our left - we have a weather curse) - we were told it is
typical to see 3 to 5 ft. waves on the north side with calmer conditions
on the west.

The island itself is lush with vegetation, quiet, no cruise boats are
docking at the present time.  Expect about as much night life as
Bonaire.  There is a Brew Pub with it's own micro brews and a Rum
Runners on the boardwalk in Christiansted and a few other restaurants
and shops are within a short walk. St. Thomas is 40 miles away, a 15
minute flight or a 75 minute ferry.
There are a couple of shops that do full and half-day snorkeling trips
to Buck Island as well.