If the Superman Dynasty can all get their hands on Green & Blue Power Rings (for limitless power) or just plain old White Power Rings then the Superman Dynasty has this in the bag, if not then the title of winner goes to The Black Lantern Corps!
The space demon Desghidorah (from the movie Rebirth of Mothra) arrives on Earth after having devoured Mars, he comes into conflict with Kurama, a nine-tailed fox demon who does not like the idea of living on a barren, dead world for the rest of eternity. The two vicious demons now stand in conflict, but who will come out on top? The Devourer of Worlds or the bane of Naruto's existence?
IIRC, Alucard is actually an Eldritch Abomination that looks like a gigantic "wave/blob" of blood and shadows covered with thousands of red eyeballs whereas Lucy is a mutant with invisible vectors that can only kill solid corporeal lifeforms. If Alucard takes on that form upon sensing that he is about to die (should it come to that), then there is literally nothing Lucy can do to stop him, he will wash over her like a tsunami and devour her soul. Sad, but true.
The Galactus Engine can operate in and attack from an infinite number of higher and lower planes existence at every point in time and space simultaneously using the full breadth of the Power Cosmic in tangent with the limitless mystical Chthonic energies it was infused with by its Many-Angled creators: Shuma-Gorath, Yot-Soter, Nyerlathortech and Kthl. The STTGL cannot do any of those things due to the fact that it was constructed using inferior technology that was engineered by mortals.
Sure it can go to the 11th Dimension, use Galaxies as weapons, etc. but it can only do these things in a single plane of existence whereas the Galactus Engine can do it everywhere and everywhen at the same exact time. Basically, what I am saying, is that the STTGL gets raped by the Galactus Engine and its crew suffers a horrific death as the giant Eldritch Abominations the GE "impregnated" the mech with tear it apart from the inside out in the same fashion as the ones that killed Aegis during the Cancerverse War.
I survived the death of a universe but was killed and resurrected several times after that. Then, during the old Light Wars thing, I destroyed myself hoping to take Earth with me. I came back from that death but as a different person, a wheelchair-bound invalid working for the greater glory of Warsman. We had a great story building up months ago but then one day all contact between us ceased for no apparent reason thus leaving my slowly regenerating character trapped in Warsdadt with no one to talk to.