Define Best...lol.
Extremely nice - and pricey would be Little Dix Bay resort - or Biras Creek(never been there) Little Dix is located on one of the most excellent beaches I've ever seen. No real diving there but looked like good snorkeling. DiveBVI has a satellite location there so when we would go in to pickup divers, we'd always see turtles diving for the bottom. We've only been to the bar at Little Dix but I'm guessing the rest of the resort was just as nice. Afaik, you can't drive to Biras Creek - they have a shuttle boat. For us they were too far removed from everything. There's another nice looking resort near Little Dix also, don't remember the name.
More reasonable would be Leverick Bay resort/marina farther north. It's a short drive from anything but a nearby small local town though. DiveBVI also has a shop there. Definitely a yacht area but they did have a nice beach area with tables right on the water. There's a couple of stores in a little strip mall on the property.
Most of Virgin Gorda is centered around the main town (the Valley?), the Baths or the LB area. Lot of areas are totally uninhabited. It's a really steep island with a lot of dramatic drop-offs to the water.
Best Diveop IMO is DiveBVI. They're really the dominant diveop in that area with several facilities, multiple boats etc. One of the few diveops that really provides the service they promote. We dropped our gear off the first day and never touched it again all week except to put it on.
The first day on the boat we were asked how we liked everything set up and it was duplicated down to fins, gloves etc. At the end of the week, we picked up our gear cleaned, dried and bagged. It's one of the best outfits I've ever dove with. Great group of people to dive with, we also hung out with them one night. They seem to really enjoy what they do. Jeff their GM is VGDiver here, his wife Casey runs the retail business - nice people. For local info - ask Finey - she runs the main diveshop location.
On VG, you have easy access to both north (Atlantic) and south (Caribbean) diving. In a week of dives, I think we saw the best of it. A majority of the dives were either in and around Norman, Cooper, Ginger, Salt Islands or at the Dogs to the north. Also we dove the Rhone - the BVI's signature wreck. Chikuzen is supposed to be another good wreck but we were blown out the day we had it scheduled. One thing I wish we would have been able to do was Anegada also - just couldn't work it into the schedule. It's a marine park and supposed to be pristine diving.
The BVI's are windy - it's why there's so many big sailboats. We rented a pretty posh villa high in the hills and it didn't have A/C. Wasn't needed, standing in the hallway with the windows open was like a wind-tunnel.
Other must do's. Rock Cafe for a good dinner, Mine Shaft Cafe on BBQ night - how can you go wrong with a restaurant with it's own mini-golf? Snorkel the Baths one day - too shallow to dive. Just about everybody, tourists, locals etc. go to the Leverick Bay BBQ on Friday night. We met people we'd dove with and some of the DiveBVI crew there.
It's easy to get to VG from St. Thomas also. Travel in that area is fast-ferry based. The ferries pick up in town or out on the East End at Red Hook. And they run often among the islands. You do need to clear customs each way.
We chartered a boat (11 of us) but friends who had to leave early took the ferry back - they left VG around 8AM and flew out of STT around 1PM. Even had time to look around Charlotte Amalie for an hour or so.
You can also fly into Beef Island on Tortola and take the ferry over. There's even a small (Cessna sized) airport on VG, we occasionally saw a plane land from our villa. I would guess from STT.