doesn't matter... sorta...

you can hook any wire to any wire (it is not like DC with positive and negative)

and normally if your prop is spinning the wrong way you just reverse any two wires.....

so You can either test to see the rotation before you solder, or go ahead and solder in any order and change the programming in the ESC
with the USB programmer it is simple... without the USB programmer.....well....I never could get it to work!

Hope that helps