Diagonal cut first is what is taught here, has been for some years. Reasoning is that once you start the cut you've set the direction, and all you have to do is line up the horizontal cut.
That is exactly why I don't like the method, you only have one chance to set the direction. With the horizontal cut first, you have plenty of time/choices to evaluate the direction and, if necessary, alter it.
Yet, bottom line, seems like both methods are essentially equal re the possibility of cutting wrong and having to recut or adjust the face. They both rely equally on visualization and estimation.