Tough call. While Guts had the unfortunate memory of the whole thing, he was slightly more "ready," having already seen Zodd, and thus, knew of the Apostles' existance first hand.
Caska however, had never seen any of the Apostles before, and on top of that, had been at Griffith's side for all of her life. She was wholly betrayed by Griffith, who she adored blindly. As strong as her will was, she had no mental capacity for the events that took place.
Guts was able to walk away from the Hawks, something Caska never was able to do. They were closer to Caska than friends and brothers in arms, they were her family.
I could keep going, tl;dr, Caska I think.