Here's why i think hulk is going to win. Hulk is probably gonna win because he has no weakness at all. Now Thanos blew up a planet that hulk was on and hulk survived thats how strong hulk is. If any hero or villain fights hulk for a long time hulk gets stronger and bigger. Hulk ripped doomsdays head off and picked thor's hammer and crushed it into pieces. Hulk has a great advantage because he can't die. Galactus probably would beat hulk because he EATS PLANETS. But that won't stop the hulk because thanos blew up a planet that hulk was on and hulk survived. Galactus has the power of cosmic energy,teleportation and telekinesis. Galactus could manipulate hulk into becoming his servant...which would be awesome.
In my opinion i think hulk would definitely win you can't kill him no matter what. The only way you can get hulk into becoming bruce banner is having betty ross to confront him because betty makes the hulk calm. Also Stan "The Man" Lee said this " No Matter who is against my green goliath there will always be a smash".