Dragon Ball Super has taken the powers of Dragon Ball's Saiyan race to the next level - and well beyond. The Dragon Ball Z sequel series started off by introducing the concept of what lies beyond Super Saiyan transformation: Super Saiyan God. Since that introducing that new concept of how GOku and Vegeta's powers can work, Super Saiyan God got its own Super Saiyan boost (Super Saiyan Blue), and opened the door to what could be a Saiyan's ultimate evolution (Ultra Instinct). However, Dragon Ball Super has not yet introduced an official canon version Super Saiyan 4, leaving fans with one big question:
Which is stronger: Super Saiyan God, or Super Saiyan 4?
At first glance you may not think there's enough information on the table to even have this debate: Super Saiyan God is an official part of Dragon Ball canon, while Super Saiyan 4 is not. The latter has only appeared in the Dragon Ball GT series as well as various games and spinoff series - none of which are canon. However, the comparison of Super Saiyan God and Super Saiyan 4 may have recently been settled, thanks to the events of the Dragon Ball Super: Broly movie.
In Dragon Ball Super: Broly, Broly's father Paragus describes Broly's limitless power and berserker rage as being the result of Broly channeling the power of a Saiyan's Great Ape form, while still retaining his human form. This unique power was achieved by Paragus repeatedly amputating Broly's tail, to stop his rampages as a great ape. So, connecting the dots of Dragon Ball power-ups, Broly is the first in-canon example of what Super Saiyan 4 power is.
Taking that into account, the question of whether Super Saiyan God or Super Saiyan 4 has presumably already been answered by Dragon Ball Super: Broly. The film very demonstrates that Broly's unquenchable power and berserker rage are too great for either Goku or Vegeta in their respective Super Saiyan God forms. Even though the two Saiyan heroes have great power and access to some unique techniques in SSG form, the serenity and cool-headed emotion needed to maintain SSG is quickly overwhelmed by Broly's relentless berserker power attacks. Even when SSG Goku has him trapped in some sort of strange energy bind, Broly simply muscles his way out of it.
Dragon Ball Super: Broly similarly makes it clear that Super Saiyan Blue isn't enough for Goku and/or Vegeta to stop Broly - although the film stops short of showing how SSG higher forms like Super Saiyan God Super Saiyan Evolved would stack up against Broly's SSJ4 power. As it stands though, it seems that a Saiyan's rage is a greater power than their higher-minded calm. Not at all surprising.