What Type of Doctor is Best at Botox?

The important factors to consider are experience, detailed understanding of the anatomy, and skill of the surgeon injector. I would recommend a Board Certified Plastic Surgeon for all plastic surgery and injections involving the soft tissues around the eye.
This includes Botox, Juvederm, Restylane, Eyelid surgery, Browlift and other surgical procedures. Board Certified Plastic Surgeons have 2 to 3 years of comprehensive formal plastic surgery training on the aesthetics, anatomy and function of the soft tissue, muscles and bone around the eye. If all other factors are similar, this extra knowledge can not be underestimated.

Many different specialties use botox and do so effectively. I would choose a doctor that can go beyond botox if needed. For example, if you really need a facelift, will your doctor be able to perform this or will you need to go somewhere else? It is nice to have a surgeon that has a concept of the overall picture and what needs to be done.

It's not about title, but training. Find an experienced Botox injector who values ongoing education and regardless of title you should wind up with a good result. Facial plastic surgeons do have the luxury of a specialty in facial musculature, but this knowledge can be fairly easily gained by other practitioners as well.
We've found that the practitioners in our area that are known for not performing injections well are the same ones that are never seen at continuing education seminars and training programs. You have to love what you do enough to want to continue to improve so ask your injector about the last time they had continuing education for injection procedures.