I was just about to repost this thread. If users that’s having problems with flavors take time to read up on flavors in this post it will go a long way in correcting current issues with mixes.
Being that taste is so subjective you can get many different views on what is best. Try following mixers that parallel your taste in mixes and see what they use.
I find as taste is subjective to opinion, there really is no “best”.
I don’t usually discriminate between best or worst, so much as reading the notes to see what sort of flavor spectrum you’ll expect to find in a flavoring, for example, banana, some may taste light and natural, while another may be describes as tasting more like the runts candy banana… really just depends what you are aiming for in your mix as to which is Most suitable* (best) for Your* mix. 
True, I suppose I should do some test batches with different brands of blueberry, greek yogurt, etc. and see what I like. Do any of you have personal favorites for greek yogurt or blueberry or any others?
I use Flavorah for my Blueberry. I haven’t tried any others, but I have no complaints with it.
Pretty much the same thing… but there are better options depending on individual taste and that’ll be trial and error. Testing many flavors until you decide what works best for you.
So what you say is true… there is no best flavor… only what a individual like best.