Take note that, if you end up splitting your visit between the two, their distance apart on the map is really not that trivial. Budget at least 1 hour to go between the two properties, especially with traffic on the 2-lane highways.

Also, the Ritz will be closer to Lahaina activities, while the Marriott is closer to town (Kahului), the airport, and Haleakala.

Wailea in general is in a drier part of the island (i.e. gets less rainfall) than West Maui is, due to the proximity to the volcano.

So, it really depends on what activities you've budgeted time for.