Hickman's highs are very high. His lows are average. His concepts are amazing. His visions for the franchise are fascinating and I'm thankful he's the creative head of the franchise. His voices for the characters (but Xavier, Magneto and Emma) feel sometimes off, and out of character.
Percy is very good, and consistent. He's very, very good at characterization. His voices for the characters are spot on. He gets them, and they talk not all the same (which is sometimes Hickman's weakness). Percy made me care and love characters I never care about before : Black Tom and Domino. He's very consistent in his delivery. His books are solid, and feel like a real team book, even if he sometimes focus on some characters, like Domino. Yet, X-Force doesn't feel like Domino's book. Or Beast book, or Loagn's book. (The opposite of X-Men Gold... Gold was Kitty's book. Kitty and her X-Men accessories)
So if I could, I'd vote a tie for both of them. But I can't. So my choice goes for Percy, for a totally biased reason : I really like the man and the writer.