Grand Destino Tower is definitely the more adult of the two. Their Three Bridges restaurant is a nice adult destination for an outdoor evening meal and drinks.
I prefer Coronado Springs pool over the Caribbean Beach Resort pool. With its pirate theme, the CBR pool is fun for children. Not sure it's the best place for 3 adults.
Have you considered the Swan or Dolphin? The Swan in particular feels more adult and gets you between Epcot and DHS, and within easy walking distance of the Boardwalk with its bars & restaurants.
Coronado has so many lounge and bar options it just seems like the best choice for an adult only trip. It has more of an adult vibe. I would choose Coronado.