The more ingredients the more problems you may have with sensitivity to one or more of the components. I like the salt and soda formula Edgar Cayce recommended. It is simple to use and comes in powder form so toothbrush bristles can function more efficiently (rather than "glued together" with excessive toothpaste).
If you prefer a paste, a small amount of Bioforce's Echinacea brand is the simplest and best formula I have found.
The most important factor however, is how you brush.