Where to go depends upon whether you will be land-based or boat-based.
I did my PADI
certification with Sail
Caribbean Divers out of Hodge's Creek, doing both my studying and initial dives at
Cooper Island (they also have an office in The Bight on Norman Island). Subsequently I've dived with Dive
BVI with success and can also recommend
Blue Water Divers out of Nanny Cay.
I had lots of time when I did this as I was
living aboard my
boat, but if you are on a schedule then I'd also recommend doing your
certification elsewhere so that when you are in the BVI you can dive the sites (and sights) instead of having to nurse a hangover while trying to study dive tables.