I think it depends on who will be using the rooms. If you have any kids, I would recommend the Dolphin. It is closer to the pool, it has the 24 hour Tubbis Buffeteria, it has the laundry room, etc. The Swan seemed more like a Romantic Getaway type place to me. So if you want romance and more adult atmosphere, I would say Swan.
The lobby of the Dolphin is much more impressive too.
Maggie