We’ve stayed at both. They are completely different properties as they are two completely different islands - apples and oranges. MFC is closer to Charlotte Amalie, closer to tourist areas and easy to access and has adequate parking. It’s easy to drive to other places from MFC on St Thomas. The beach is smaller and has an active waterway past the ropes. I wouldn’t swim out past it. At busy times it was hard to find a pool chair. They had activities on site. The pool was small and can be busy at times. The rooms were comfy and the kitchens were quite large.
WSJ you have to take the ferry to and has nothing nearby. It is a 30-40 minute walk to Cruz Bay, otherwise it’s $5/person for taxi each time. WSJ is quieter but we found they had better fun team activities since the location is more remote. The pool is quite large and pool chairs were always available. They had bobbing for beers in the pool and my spouse won a handle of Cruzan for their dance contest. WSJ has an on-site winter sports company and can rent SUP, kayaks and Hobies.
Both are fabulous resorts with their different strengths. I hope that helps!