To add/clarify, the Sheraton and the Westin Maui Resort have a resort fee (even on free nights), while the Westin Ka'anapali Villas do not.

I spent a week at the Villas last month and for our family (which included two young children), it was the ideal SPG property for our trip. All things being equal, and they are since you are using FRN's, I personally would choose the Villas again. Then again, a lot of other factors that are likely different for you (i.e. who are you traveling with, what are your interests, etc.) should play into the decision.