It's possible you might find something for March at either resort, but I wouldn't be at all surprised if nothing is available. Most members book between 7-11 months out.
If you're looking at the lowest posted price for BWV, that's probably for standard view villas, which are almost certainly gone at this point. There are few of them, and they get snapped up immediately by members because of the low point cost. Use the cost for Boardwalk or pool view villas as your estimate.
As for choosing between the two resorts, the big differences in amenities are that BCV has the more elaborate pool complex, and probably a larger selection of restaurants, because you get both Beach Club and Yacht Club's restaurants. BWV's restaurants are outside on the Boardwalk; BC/YC's are indoors (except for the pool bar, of course).