I was literally thinking about this yesterday. My favorite stage of bow building is chasing the back ring. It's oddly satisfying to me. I also love looking at a stave and visualizing the bow within, and carving and filing it down to the desired front profile. Oddly, I don't enjoy drawing the lines for the profile, but I like following them to layout the bow.
My least favorite part of bow making is when I break one haha. I also hate making strings, but each bow gets a new string made for it for a good custom fit. As said before by at least one other, I find making arrows boring.
I also appreciate that each bow teaches me something, even if it breaks. It can only serve to make me a better bowyer. I'm enjoying reading about everyone else's favorite and least favorite part, thanks for asking and thanks everyone else for sharing.