Agree with all you've shared here. I'd agree that the beaches along this coastline aren't the best of Mexico, but since we're traveling from California, we want to minimize travel to have more time once there.
From what I gathered it seems like the Westin and Marriott could likely be overall better properties, but to your point, they can't beat the Sheraton's close proximity to some of the more interesting neighborhoods (as well as restaurants). Location seems to be the one reason I am leaning towards it.