I liked Gareth's death more, just because of the coldness of the whole thing.
Joe's death was awesome, no doubt. But it was reactionary, it was Rick finally snapping and embracing the dark side of himself.
But Gareth, that was just fucking cold. Deserved, but cold. The way he mocks him, circling him. His dialog completely devoid of emotion. "We didn't want to waste the bullets."
"No sense in begging, right?"
That whole scene was just amazing, a man who went beyond his breaking point and was forever changed. He would go through these moments throughout the series where he would try to balance himself between being a brutal savage and being someone who tries to rebuild the world. But in that church, facing that enemy, he was completely cold, ruthless, and emotionless. Just a killing machine.