I have tried many many watermelons... I think that Tasty Vapor is the closest to the Jolly Rancher Taste. My GF only vapes watermelon, cherry and Pina Colada...
Apple... my three favorites are: Appolos Apple from Vape Safe, Backswoods Brew and Digitalcigzz apple jaxx
yes... Vapor Bomb's is also quite good... forgot about that.
Alien Visions (avejuice.com) has both a tasty watermelon and an Apple Teaser flavor that I like.
Haven't tried these, but I have heard really good things...