Yes, I will echo the previous people's posts that generally, a resort restaurant is your best pick for quiet. And Victoria and Albert's is the ONE guarantee of it (unless harp playing bothers you).
I have eaten in just about every park restaurant and it totally is pure luck how noisy or quiet any of them can be on any given day. Like, my last dinner at Monsieur Paul was incredibly noisy, which you wouldn't think, but all it takes is a few boisterous tables and there you go. It's like 50/50 when your talking dinner at the theme parks or maybe like 70/30 in favor of noise at dinner time. Lunch is maybe 50/50 and yes, I have had quite a few quiet meals at Coral Reef, particularly if the lunches were 2pm and later as a previous poster said.
Spice Road and La Hacienda de Angel were pretty quiet as well because they are the 2nd tier restaurants in their country's pavilion and thus you have better luck of a more quiet meal, again, especially at lunch. Rose and Crown has been quiet too, for me, but again, it depends on the time. I recall Skipper Canteen was quiet too, and not very crowded at both of my munches. Even SCi-fi DIne-in tends to be quiet because it is in the dark and people are watching the movie screen. Hollywood Brown Derby can be quiet too, depends how busy it is.
Tiffins is a struggling restaurant and will almost definitely be quiet since there will be next to no one in there which is my sense of it, at this point - it's just too expensive and seems to me, to have been a miscalculation to put a signature restaurant like that in that location in Animal Kingdom and there is just too much far more affordable dining choices there, both quick-service and 1-credit sit downs/buffets and the more popular well-known elegant restaurants at the Lodges are just a quick bus-ride away, but anyway, Tiffins is bound to be quiet - LOL when I was going to my meal there last December, there was a poor cast member outside of the entrance whose job it was to parade around and twirl a huge sign announcing meal coupons and discounts to try to entice people to come in to eat there - I HAVE NEVER SEEN SUCH DESPERATION to get people to eat at Disney - but I imagine this was quite an investment for Disney are they are trying to save it. Food is incredible, by the way.