what is the best part of being a doctor in an emergency room?

I think that you would get a different answer from everyone you asked. For me, I like the freedom to practice in an environment where insurance, etc, is not something I worry about, I like the high stakes environment and adrenaline rush, I like the variety of complaints and never knowing what will come in next, and I like opportunity to work with patients from all walks of life and physicians from (almost) all specialties. That said, there certainly are things about the job that make it difficult as well.