As DG alluded to above, I think the fly will catch the most fish is the one you fish the most. It's chicken and egg thing -- do you fish it a lot because it catches, or does it catch because you fish it a lot.

Look at the other end of the spectrum: I've personally never caught a trout on a wooly bugger. Obviously they catch trout, but I only try one when I have already not caught fish on flies I prefer. The chances of a wooly bugger working when I've already not caught fish on at least several wet flies, several dry flies (or several nymphs, depending on conditions) and several streamers in which I have more confidence are pretty slim.

OTOH, flies that have miraculously caught fish after I've gone through my whole repertoire of usual suspects raise my confidence in them sufficiently that I'll fish them more, and therefore catch more fish on them. It's a vicious cycle. That first fish could have been pure luck, but the fly will get fished more.