>>528188269
Assuming the question is whether to slot another green or a red tau, it barely matters. If you go from 100%+192.5% damage done to 100%+200%, your total damage increases by about 2.5%. I really doubt you'd notice a difference, unless you want a nice round number in your buff display.
At that point I'd rather slot duration especially if I'm running two buff abilities. But you can really just do whatever. It doesn't really matter that much.