I've stayed at both BVC and at OKW. OUr BCV stay was a December one that was too cold to swim. My family actually prefers OKW, but here are some thoughts:
OKW advantages: Larger rooms than BCV; cheaper; ability to park in front of or very close to your unit; new pool slide, boat to DD.
OKW disadvantages: Very spread out resort with several different bus stops
BCV advantages: Stormalong Bay is an awesome pool area; the ability to walk to MGM and Epcot; availability of restaurants in the near area
BCV disadvantages: farther from the parking area; smaller units
You may also want to ask this on the DVC board, as that board is very opininated as to these two resorts.