I prefer the Dolphin, especially in a renovated room. The Dolphin lobby is cooler, has more kid-friendly amenities, and it's a little closer to the pool. BUT this trip I'm staying at the Swan because the Dolphin wasn't available all our nights. The Swan is completely renovated, and it's right next to the Dolphin.
There was a convention going on while we were at the Dolphin last year, but you really didn't notice it. I actually think the Swan has a more "business" feel to it.