They are very different, and each has their charms, and their shortcomings. When I go to Maui, if it's for 6 or more days, I try to spend some time in each area. My last trip, I spent 4 days at the Westin Villas in Kaanapali, and 4 days at an AirBNB in upcountry Wailea which is run as a small Inn, near the Hotel Wailea (I would only recommend this if one has a car - in which case it's fine). I basically chose this second alternative because it was about $150 per night all in, which I considered to be noticeably cheaper than the 40K Marriott points + resort fee that the Marriott would have set me back.

The 4 nights in the Westin Villas was a swap from the timeshare I own (a week in the Westin Kierland in Scottsdale in August - which trades evenly for 4 midweek days at the Westin Villas in Maui in peak season) BTW, I have NEVER used the Westin Kierland week in August as it is - I ALWAYS swap it for 4 days in either Kauai Princeville or Maui during peak season (I've done the Maui swap 5 times, and Princeville twice and never had a problem getting availability in Hawaii between January and March). Which is a nice trade considering that the Hawaii timeshare weeks cost about 5 times what the Scottsdale week cost me.

That being said, if I was planning on using my SPG or Marriott points for a Maui property, I think that the Marriott Wailea is the best value between the two programs (although, if traveling with kids, a case could be made for the Residence Inn in Wailea, since it has no resort fee, free breakfast and the rooms are really all suites with full kitchens) But be aware that the Res. Inn is not on a beach, rather is about a half mile up the hill from the beach.