A friend asked me which one is the best teleconverter and if there is much difference between them. I had to admit that I didn't have a clue... Is there a comparison anywhere of the more popular ones? Canon III, Canon II, Kenco, Sigma, Tamron ?????
There are not many serious reviews about teleconverters. But I've heard several people in Canonrumors, saying the Canon III models combined with the new Canon teles has higher accuracy and speed of AF.
The Canon MK III is definitely better. Tamron and Kenko are very good, they are the same TC. The sigma TC seems to be doing well when used on Sigma lenses.
It really depends on the lens you are using, Kenko / Tamron /Sigma will mount on some lenses that the Canon TC's will not mount on.