In the comics Galactus simply isn’t a villain and I don’t want them to make him one like they did with Ronan. Kang would be cool as there lots they could do with him that would be very unique.

They could also have Annihalus and his Wave; bring back Ultron and have him become a cosmic level threat; or maybe do something different and have Norman Osborn being both the Green Goblin and the leader of the Dark Avengers with his own Iron Man armour. He would be more of a political opponent would be a dark reflection of Fury, doing little cameos and recruiting the Dark Avengers (Abomination could be a member).

Mrriddle0

While galuctus while may not be a villean he would be a good way to bring all the hero's rogether again a long with this. he galuctus would help explore the backstory between the infinity stones and coiled help bring in or explain the clestials.in guardians of the galaxy you see a celestial destroying a world along with the this ego said he was a celstial.While ego may not be a celestial he mentioned them confirming them in the mcu so how better to explain the backstory of the stones Bring a new bad guy in a new big bad guy in and introduce more characters

Lastly gualctus may not be a villain. But in the eyes of the people of earth who don't know why galuctus is trying to eat planet earth.would you think a person eating your planet is good without knowing a good reason why.

I suppose they could do what they normally do in the comics and work with him to find uninhabited planets and in the process learn that he is actually very much a good guy and then work with him and his herald(s) to stop another threat. Like what happened during the Annihilation Wave.

Mrriddle0 that would be good in my opinion

Doom gets introduced in an earlier movie, has presence in a few including an FF movie, leads to Avengers event where they think the big bad is Doom, the cliff hanger at end is the real Doom has been imprisoned and the actual big bad is Reed Richards posing as Doom. Because you just gotta do a good guy gone super bad now and Richards is perfect for that, a la Ultimate Uni.

I am gonna say that the most logical choices for the MCU Big Bad are either Doctor Doom or Galactus.

Korvac would be a nice villain and I think it would really boost his popularity

Doctor Doom would be a great choice if there going to include Fantastic Four into the MCU.

^Yeah that isn’t happening, he isn’t even in the MCU as of right now and I doubt that’s going change looking at then recent news