Depends on how much water you want to use, the blue ones are about 1mm the green ones 1.5mm, its also complicated with the spray pattern and an all round spray pattern is slightly bigger that a 45 degree pattern. I find that 4 blue jets is fine for me - using about .5L/min
I used to use the green ones and they may suit those wanting more flow. Remember though that you will need a by pass to reduce the pressure or once you have found the right combination simply a spot of superglue to hold them in place, they will spray out about 6ft if you want. You will also need the Ts connectors for each jet. Use the Algarde 4mm hose or the Raindrip vinyl. 1/4"