It's really hard in II to get prime weeks. You can get off season weeks fairly easily and those weeks can be in ultra prime resorts such as Marriott and Hyatt but it is really hard to get the prime weeks. II has preference periods, which you can't get around. Marriott owners get first crack at the best Marriott weeks and Hyatt owners get the first crack at those weeks and Westin/Starwood get first crack at those weeks. As a result the best weeks are simpley never available to outsiders. Since you do not own a Marriott or Hyatt or Satarwood/Westin week, I would stay in RCI. You can try II, but I think you will always be on the outside looking in.
I own both Worldmark and Marriott weeks. My Marriott week can pull some amazing trades. My Worldmark week can't pull anything for prime season, at least not at a Marriott or Hyatt or Starwood resort.
RCI doesn't really have preferences, like II does. It is much easier in RCI to get a prime exchange than in II. Hope that helps and good luck.