Ahlusion. Hands down. Explore the website and you get an idea why.
I keep wanting to use up old bottles of previous favorites and I seem unable to go back with pleasure. Except maybe Highbrow's Limoncello which I think is really especially excellent. And all that's just me. (Haven't tried Ahlusion's lemon flavoring yet, so dunno if even that fave will hold.)
But there's not a "break out only for special occasions" juice - the price/quality range isn't that broad. Great and interesting stuff, ejuice, but it's not cognac.
Anybody who wants to sell a bottle of juice much outside than the current range had better have a grape press in his back yard, nubile grape stompers, a big copper kettle in his kitchen and possibly a tobacco field. And price is no guarantee in this game - there are some vendors out there asking biggish prices who are really just doing a fair job of jazz-labeling the usual commercial flavorings.