I also would say the Yachtsman Steakhouse. It's has great atmosphere, the interior is wooden, romantic lighting and overlooks the pool at the Yacht and Beach. They just were rated the #1 Signature Disney Owned restaurant on property. It is a hidden gem in it's own right.
We have gone there 8 times over the last year and have always had a great meal and service. The Chefs and Managers there still understand the meaning of Disney Guest Service.
Don't forget you can order a special cake for your dinner also. The Pastry Chef for the Yacht and Beach is awesome, I've ordered 6 cakes this year and they have been moist, rich and just really really good. I have a very picky 5 yr old nephew and he LOVED his birthday cake from there.
Have a great time where ever you decide to celebrate your special occasion.