Hi Stuart,
I think the ideal is probably to have a combination of two, more to get the best out of both sexes. I'm certain that Widowhood is the best method to consistently fly well with cocks but I'm equally certain that hens are best on natural. We only fly natural and have 8 positions in the top 5 of the open result in national races from 500 miles - 612 miles but only one was achieved by a cock - evidence that natural suits hens better. I do feel that our cocks are slightly being wasted by this system but i couldnt stand to not fly the hens so we make our choice and get on with it. Perhaps with umlimited time and space I would try to work both methods concurrently.
I would suggest the more important thing is to have good distance pigeons first and worry about the system second.