Tyrant. Onslaught never even close shown the real power he had because of Franklin. If this is true and had all access to Franklin powers, he should win, but from what we have seen, Tyrant wins with ease.
I have a hard time seeing Tyrant damage Onslaught. It took a very enraged Hulk to just crack his armor. Onslaught casually penetrated Juggs like he was made of jello and slung him across the continent. This is well beyond Tyrant.
DP Tyrant didn't do anything to Galactus but get embarrassed. When Tyrant started absorbing Galactus energy that's when the tables were turning. But that's isn't DP Tyrant anymore.
Juggernaut is way more durable than Galactus. Onslaught pierced him with relative ease.
Way to ignore context. Tyrant fought a FULLY FED Galactus on Galactus' home turf. Neither of them were doing anything to each other and Galactus was the one to panic first and cheat to use his machines.
This is what happened in the lead up to their final showdown -
Galacuts RESPECTED "DP" Tyrant's power and ordered Morg to find him a world to feast on because Galacuts would need ALL of his power to face down Tyrant : (please log in to view the image)
Morg finds him a world ripe with biospheric energy and Galactus says he hasn't felt this powerful in ages : (please log in to view the image)
This was the powerlevel of the Galactus Tyrant faced off against. Yet it was Galactus that blinked first and attempted to cheat by using his machines vs Tyrant. It backfired spectacularly.