You will 100% have a better selection. Steakation has great quality, but is expensive.

If you are doing a big shop I would personally recommend taking your rental car from Virgin Gorda on the car barge (check with the company to make sure they allow this). I have found it much easier to load the car up and drive it straight back rather than ferry to Tortola, shop, unload all the bags from the car, load them onto the ferry, then unload them from the ferry and back into your car on VG.

If you are up for it I would recommend going to Rite Way, Bobby's, French Deli and Steakation. With those 4 stops you should be able to find good quality most everything you need.