If you're trying to get the most out of each leve, it seems the triple turn ins are still the best.
If you're trying to level as fast and cheap as possible, it seems the single turn ins are still the best.

Quick Synth now gives the same XP as making the item with zero quality yourself. When I don't actually have time to play I'll just QS a pile of leather, or lanolin, or potions, or any one step synth that I can just blow some leves on with absolute minimal effort.