Worst was Marlboro generic from Cigabuy. 50 ml for $2.14, I knew it could be bad but what I didn't expect was something that I'm not even sure is safe to throw in the trash, or do I need to take it to a special toxic waste disposal facility. They're still selling it too. Many positive reviews for it, mostly foreign and nonrecent (tip: filter reviews by "Most Recent", you still can't see all of them by any method??). Closest smell is contact cleaner (isopropyl and hexane).
Of legit flavorings, V2 coffee I couldn't stand, and a full cleaning of the device was needed to get rid of it. I detected some of the same in Hangsen Golden Tobacco and Desert Ship (not their Highway).
I had a run in with my first bottles of juice. Carolina Flavor.
They actually have their own chain of shops, although in fairness what I bought was cheaper and looks diff. than what's on their website now. I tried the Tobacco and RY4. The RY4 isn't bad except clearly whoever made it had no idea what RY4 is. The Tobacco was very strong with the flavor I call "old shoe" (actually useful in proportion maybe, but this could be used as flavor concentrate). I once got HotVapes 555 which also tasted mostly of the stuff. Loaned it to a friend whose dog tried to eat it (got sick but recovered or it wouldn't be funny). Couldn't figure out why the dog did that until I realized: they like to chew on old shoes!
Some other losers (gas station brands?) were Haus and VaporX.