Top 10 units for a QCK Team (in no particular order).
Captain Ability: 2X ATK & 2X HP to QCK units.
Special: Nullify damage from DEX enemies for 1 turn.
HP: 3300. ATK: 987. RCV: 231.
Jozu has a very powerful special, but when he's captaining a QCK Team, he probably shouldn't be facing off against too many DEX enemies.
Boa Hancock: 10/10
Captain Ability: 2.75X ATK to QCK and PSY while HP is above 70%.
Special: Delay enemies by 1 turn and heal.
HP: 2860. ATK: 1320. RCV: 515.
Boa Hancock provides an incredible boost and an incredible special and incredible stats. She's an incredible QCK captain, as she should for being a 6* unit.
Captain Ability: 2.5X ATK to QCK units.
Special: 15X QCK damage to all enemies.
HP: 2886. ATK: 1020. RCV: 279.
He's simply a QCK boosting captain with really no other good benefits, but 2.5X captains are still powerful.