We have seen both resorts, but not stayed in them.
Bequia Plantation House would be my first choice. It is close to the heart of all the best of Bequia: restaurants, beaches, and an easy walk to the town on the boardwalk.
Bequia Beach Resort is on the other side of the island, at Frendship Bay, and more remote.
Bequia is a small island but a true gem.
Good luck with your decision!