For the top valves I prefer (and have basically settled on) barbed 6mm brass nozzles. I will modify these with bits of tube and plastic straws though. https://www.dropcontroller.com/equipment/#Nozzles
A short while ago I did some small collisions and needed more delicate drops and used the 4mm barbed nozzles but this was a one-off. I normally find these too small for the collisions I like.