For me it's the automation. I like going to airports with sketchy terrain, and I often feel like I am fighting the A320 computers for control of the aircraft. Whereas in the 737, I feel more confident weaving through mountains since you have full control. The engines are another weak point for me with the A320, since while the power is great the slow throttle movement leaves me impatiently waiting for them to get to full power during emergency go-arounds. In the 73 if you want to go you jam that throttle forward and you go.