I'm a helper--a people person. It's what I do. It's ultimately why I chose my profession. So, that would be the best part for me.
Probably second would be the variety of interacting with different individuals which is also what I love about my profession. Each day, heck, each class period, is fresh and new because of the interactions with the individuals in my classroom. I'd be miserable in a profession where I did the same thing all day and didn't have a variety of people to constantly interact with.