My 2 favorite apples are FA Fuji and INW two apples. I sort of go back and forth, the INW being a little more like apple cider but wow is it good.
I was on a quest to find the watermelon used in one of my favorite store bought brands. I bought 6 different brands of watermelon and made testers for all of them. I wasn't able to find the brand, of course it was the one I didn't buy, Capella Sweet Watermelon, I bought the Double Watermelon.
Here is the thread were I conducted my test:
http://vapingunderground.com/threads/watermelon-flavor-reviews-and-favored-percentages.132716/
Looking back at my notes I felt the INW was the most natural tasting at 3%, but any higher than that and the flavor fell apart and it became my least favorite. FA is really good but doesn't come alive until about 5%, natural and tasty but a little sweeter than I was expecting.
For watermelon I am partial to CAP Sweet Watermelon because it is what is used in one of my favorite juices. It is not the most natural tasting though, it leans to the candy side. LA Watermelon is another favorite of mine when I want the Jolly Rancher Watermelon flavor, just make sure you get the clear version with no food coloring.