Like it was said above, it depends on your situation and what you plan to do. Also your personal beliefs. There are some who don't believe in the use of bits. Meh.
My mare is bitless by her own personal choosing. I was told when I bought her that they only rode in her a rope halter with no issues and I attempted bits of various styles and was met with a very angry horse. Took it away and no problems. I plan on training my coming 3 year old with a bit though.