There's a guy who has spent a lot of his life tracking down apple cultivars before they go extinct or lose their genetic uniqueness, I forget his name but he is definitely an authority on the fruit.
Been a number of years since I listened to his interview, but pretty sure he said the tastiest apple he's ever come across was one called Sheep's Nose, also went by Black Flower apple I think. Northern PA I want to say? They have an odd shape to them (very top heavy) but he said they are more fragrant than other apples but with less flesh. Baking them in the oven is apparently a transcendental experience for an apple fan.
I saw some Cosmic Crisp and grabbed a bag. Flavor was good, very loud and crunchy to eat, but it just seemed like a Gala with a slightly thicker skin to me. Not sure if they're worth 3.99/lb when I see Gala and others at 1.79/lb, but I'm going to keep trying ones I've never had before.