Hi Tami. The best organization will be the one that fits your needs both from a business perspective, financial perspective and liability perspective. Over my 19-year training career, I have literally had all of the various business organizations (I started out as an S-corporation, then went to a C-corporation, and finally settling on an LLC). I think that each of us as trainers and business people have different needs and so spending an hour or so talking with an accountant and attorney before setting up your organization would be best in my opinion.
I hope that this helps.