Shi'ar. Easily. They already annexed the Kree empire after the Shi-ar / Kree war and even ignoring that the Shi'ar probably outnumber the other two empires combined (at that is using Skrull empire was at the height of its powers, not the non existent one that exists now).
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Just surviving isn't the same as winning an all-out war, though.
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The Shi'ar hold a lot more territory than the other two. The only reason the Kree were able to hold them off recently in War of Kings is a combination of Inhuman help for elite forces, the Shi'ar not giving up on other military activities until well into the war, and finally Shi'ar internal conflict.
THe kree suffered the greatest casualties in the annihilation war and half of their territory is occupied by ravenous. And the Phalanx isolated all of kree space and wreaked their havoc. And that was before they tangled with the shi'ar.
Yet they still are sending a huge fleet to attilan. I don't call that surviving, i call that thriving.
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