Gohan Beast becomes the climax of Dragon Ball Super: Super Hero and Black Frieza functions as a last-minute surprise in the manga's prolonged fight against Gas. These two threatening transformations have yet to meet, but there's some interesting evidence that indicates who might be the strongest.
Hypothetical power rankings from the Dragon Ball community can only go so far. However, it's significant when Toriyama himself confirms a detail or expresses it through a revered character in the series. The Oracle Fish is a rare individual who may not look like much but is actually one of the most prophetic characters in the Dragon Ball universe.
The Oracle Fish coyly implies that his recent prophecy where a new individual emerges as the strongest fighter in Universe 7 might actually refer to Black Frieza. It was initially thought to be a reference to Granolah, but not anymore.