With II, you can exchange for Westin's and Marriott's, which is really a good thing if you like Hawaii. The Westin's & Marriott's are on Oahu, Kauai, & Maui. And then there's Cancun, Aruba, St Thomas, Spain, Paris, Thailand, St Kitts, and all of the other Westin's & Marriott's on the mainland.
With RCI, the best you have is HGVC and Disney, but RCI enforces a 1-in-4 (year) rule with HGVC. Disney is very hard to get into.
With II, you don't have to worry about RCI TPU's, which is a good thing.
Also, exchanges are cheaper in II and they have a new Re-Trade option, where you can re-trade up to 3 times for a one-time $49 fee.
Go with II.