I am thinking that 9-60 Improves on burst resists, then power is lower,  but 3-60 gives more power and balance, so I don't know which one to put it on.

3-60, it generally make it focuses attacks more on the three wing blade

I’d go 3-60

I am thinking that 9-60 Improves on burst resists, then power is lower,  but 3-60 gives more power and balance, so I don't know which one to put it on.

3-60 or 1-60. The whole point of Phoenix is aggressive, in-your-face x-dashes to score knockouts. Even 7-60 would be better if you want to add more weight.