We've done both and you won't be disappointed with either. Our personal preference is YSH because we love the steak there and the atmosphere and service is great as well.
We haven't been to Narco's for quite a few years--it was noisy and other than that I don't remember much about it. YSH has become a favorite of ours because of the quality of food, service, and the atmosphere is calm by WDW standards. I'd try Narco's again, but YSH is definitely the superior choice for us.
Another vote for Yachtsman. We were at Narcoosee's in March and while the food was wonderful the service was awful. I have honestly had much better service at Dennys.
Also voting for YSH. The atmosphere is more fine dining and quieter. Narcoosees is noisy and if you like fish/seafood, Flying Fish is much better food.
Another vote for Yachtsman. We were at Narcoosee's in March and while the food was wonderful the service was awful. I have honestly had much better service at Dennys.