I personally will choose the Canon 1.4x for sure. I have had a 1.4x in my kit and it performs excellent with my 70-200L. But more to the point is that I would prefer the brand to match especially in this case because I do not want to take a risk on capability issues and focusing accuracy and speed. Those seem to be more valuableto me. Plus the Canon 1.4x is not that badly expensive, peace of mind is worth something.