Ego. Ego can go Super-Ego, which has been enough to stalemate Galactus, and even if he stays in regular Ego the Living Planet form, he has taken blasts that focused the energy of literally millions of stars and shrugged them off. The Deathstar is likely not even the most powerful superweapons in the SWU, witht that title going to Sun Crusher for sheer destructive potential, or the Star Forge, for utility.
Talk about stupidly overpowered ridiculous character.
The Deathstar is very powerful, considering it can obliterate the mass of an entire planet in under a second. I don't think people realize just how scientifically radical that alone is. To say some living planet can absorb more than that is really off the wall.
Ego has shown to ability to humiliate an opponent who rips stars in half, flys through blackholes, and has matched Galactus, who destroys galaxies when sufficiently powered. He has taken attacks that literally focus the energies of millions of stars, and has shown the ability to transform into a more powerful state known as Super-Ego, which is nigh-omnipotent. So yes, he should be able to take on the Death Star.