What is your swing speed/style? If it is long and aggressive, try the PK Black Ace 90.
I have my HS #1 playing one now instead of his Kfactor. His serve has more pop, his volleys are better and his strokes are no longer flying like they used to. I have him using Big Hitter Silver at 48lbs.
PK "Pro Boron" w/Big Hitter 17 Mains/Liberty 16 crosses is money!!!
The PK "Copper Ace" w/gut ain't shabby either!