And further, Koinzell is tortured the entire time because he sees all the good that at least Glenn did, and he still carries out his revenge. That, and as g-value said, with each "hero", he's remembering the good times they had, and you can tell it seriously hurts him each time he kills one. He's set on his revenge, and there is definitely satisfaction in carrying out his revenge, that sort of cliche empty satisfaction, but there's also great sorrow. The thing is, he's killing his friends, and while he hates them deeply with the very core of his being, they are still his friends.
Gatts (I can't call him Guts, it feels weird to me haha) on the other hand is really just a berserker. Sure, he cares about the people around him, and he cares greatly for Casca, but that means nothing to his rage, and rage is all he feels towards Griffith so far.
Even with Koinzell's first kill, he cries, even though he doesn't regret it at all, it's still very sad for him. I don't think Gatts's pain really compares since he just drowns himself in rage; Koinzell takes it all in.










