Swan, though both are nice. They are acutally very similar. They share boats and pools.
Buses come to Swan first and drop off there first.
Not sure if this is still true, but Swan used to have bigger beds.
Swan has better views.
Swan has double sink outside the bathroom, I can't recall if the Dolphin only has one sink, or both are in bathroom...but there is some difference in the sinks that makes Swan better.
Rates at Swan are slightly higher.
Dolphin has both QS restaurant (refillable mugs)and laundry facilities. The Swan kind of has a QS place, but it is only open in the am.
The Dolphin is slightly closer to the big pool (and there pool area has a better poolside dining/bar area)
I know they have changed the restranuts since I was last there. Only the Swan has a character meal.