Depends. Are they or not under some mental influence?
If they are not, I'd say Beak.
If his wife and kids are still depowered, he maybe not feel comfortable with mutants taking the "homo superior" thing very litteraly. Could lead Tito to consider himself superior to his siblings.
Other than them, Surge, Transonic, Quire and Hellion are probably the most rebellious among the kids, for different reasons.
We already now that Pochie is in X-Force.
Hellion has always been a mutant > flatscans kind of guy, so he must love the current status quo.
Surge has been so fed up with all the deaths that she is probably delighted with the Five resurrecting mutants.
So Transonic would be the most likely to leave, especially if she feels that Hope has another crisis of "messiah complex"