i've only used zambon, and BD and IP for orals, but i heard from some guys i trust (some are a few vets on this board) that the QV winny injectable is actually top quality just like zambon. i wouldn't use vet gear personally though.....cept EQ of course .....so i'd use zambon myself, but i could be swayed by the price and the reports i've heard on QV very easily.
The QV 50mg Stan is actually a very good product, better than I expected, but NOTHING beats Zams. If they're available and real then I wouldn't hesitate.