In all seriousness: I LOVE Maui and have never been to Cancun, but what Podaar says is correct. If you want to kind of be independent and do a lot of different tropical outdoor things that you can drive to, Maui is absolutely incredible. If you want light life and want to be catered to in the all-inclusive resort format, Cancun is your best bet.
For Maui, here are some thoughts:
1. Get this book:
https://www.google.com/express/product/4598454375886011087_1706242250857780715_8636635?mall=EastBay&gclid=CKD2p5P9n8wCFRVsfgodi-EBIw Just do it. We did the first time we went, and it was fantastic for its thoroughness and descriptiveness. Whatever we wanted to do, it helped us make sure to find what we were looking for and maximize our experience with a lot of knowledge we would not have otherwise had. One thing I will say, however: It really hypes this one particular off-the-beaten-path, little-know attraction known as the Olivine Pools. That place is definitely worth seeing. However, be VERY careful there. The book does not highlight just how dangerous that place can be if you are unaware. See here:
https://mauiguidebook.com/adventures/olivine-pools/ As the lead-in on that site says, "Be Very Careful Here - People have died here. Many more have been injured. Understand why, and don’t be next." But still worth seeing if you are aware and careful. By the time we left, the book was written all over, pages were folded and dog-eared, and both us and the book were worn out. And it was so worth it!
2. Unless you really want the 5* resort atmosphere, save money and rent a condo. You can get a really nice place in Kihei, for example, that is right across the street from the beach at a fraction of the cost of a resort. And if you want to prepare some of your own meals, they usually have a kitchen, and you can save money on food by shopping at the local Costco, Walmart, and supermarkets. We did this and would cook our own breakfasts and make sack lunches for our excursions, and then not really even worry about the cost of dinner when eating out because of the money we were already saving.
3. Rent a car and make a point of spending several days getting out and seeing the island. It is incredibly varied for such a relatively small island and really has a lot to offer.
4. Check the weather forecast as soon as you get there and plan accordingly. One of the things a lot of people do is go up the big mountain that is there and enjoying, among other things, sunrise or sunset from the top. On a cloudy day, you don't really see much and end up missing a lot. So check the weather forecast and plan to do it on a clear day early in your trip. The reason I say plan it early is because the weather changes frequently, so you may think you have a clear day, and it can change on a dime. Leave yourself room to reschedule for another day just in case.
5. World's best banana bread. Find it. Eat it. Love it. Trust me on this one.