Ok, with sargeras getting a MASSIVE ass 2-A buff, along with the fact that Goku has SSJB with kaio-ken in the mix now. I'm going to makes a pretty long post as to why both could win or lose.
But first off, the winner is EASILY sargeras. However, that's due to a few reasons, not just 1.
1. Goku has known issues about lowering his guard, while giving his opponents second chances. He's to soft, and he's too...good hearted. Sargeras' mission is to destroy ALL life, if he looks at a lifeform trying to fight him, he'll have no trouble giving him/her a taste of the legions might. So...goku is clearly lost here.
2. Ki is life energy. While that might not sound like too good a reason as to why sargeras should win, the affect gives this match a MASSIVE ASS TURN! A. Sargeras' legion has the ability to take away soul magics for themselves. Meaning, if someone were to use something such as KI towards a demon with their life energies and all that, they'd fail due to the legions soul drain abilities. And if his legion is able to do that, then..well...he has the power to drain souls as well.
3. Idc about what anyone has to say ANYMORE, sargeras 5v1d the GODS of the WC universe. He easily took down aman'thul (who is most likely the one that created all timelines and multiverses), while having enough power to create a fel-storm, ripping the physical bodies of the pantheon EASILY! And even though their spirits are now inside the keepers, they're inactive, and..well...norgannon (the titan that originally ran away with the souls), is 100% dead aswell. So...whoopidy ******* doo I guess. Goky has trouble standing against 1 god, so why comppare him to this guy?
4. he's a living flame world that is able to rip through reality, while destroying galaxies, while...most likely having the powers to destroy multiverse. And the only reason as to why he's not here yet..is because of the fact that his spirit is in the nether...waiting. Goku, while being able to cross from 3-B to 3-A, has no stand against guys like Zeno (2-C), and remember....sargeras as of NOW is 2-A. So....yeet.
Sargeras still wins by 100% hax.