Catherine the Grape
Sour Skittles
Granberries
Velvet Cloud is my absolute fave, been vaping their Beards for over a year. I'm very allergic to PG however so my opinion is biased. Their juice is the only one I've found that I can consistently vape without issues.
I see a lot of fans of their tart flavors and thought it was worth mentioning. I'll be getting some Granberries in a few days so I'll check back with an update then. Oh, and you get a free 5mL sampler with every purchase so you can try at least 2 of those flavors out for like $12.50 total (which includes shipping). They've also got a 20% sale going on right now just use the code 'PRESIDENT'. Just make sure to specify which sampler you want at checkout!