Although I think the food and view at Ca Grill are the best of these 3, I would pick Citricos for most romantic and my reason for this choice is that CG and Narcoosees tend to be a lot noisier which I do not find romantic at all.
Hope you don't mind as we can only offer comment on CG and Narcoossees and perhaps the Coral Reef ; we haven't made it to Citricos yet but lets hope the pound recovers a little against the dollar!
My DW and i are split on the CG and Narcoosees debate and when we discussed it , we thought that the Coral Reef was another option. My DW also reminded me that there is the Wine room at CG which is off the main dining area and is a very pleasant discrete space.
I'm sure you will have a great meal whichever you choose - have a great time!