Since my former poll post about these two apparently got deleted.
Darkseid, the ancient tyrant lord of Apokolips and emanation of extra-dimensional abstract concept of tyranny. Aside from having strength comparable or superior to Kryptonians, Darkseid can fire self-tracking transitional phasing blasts, which can archive multiple effects, from atomic dissociation, existential erasure & restoration, to manipulating time and space. However, they can be resisted by Doomsday and Superman. Darkseid also possesses psychic powers, such as telepathy that allows him to invade minds from another dimension, and is supergenius in terms of intelligence.
Fernus, a Burning Martian and malevolent consciousness locked inside Martian Manhunter since millennia. He has standard Martian powers, like telepathy that allows him to scan minds of entire planet population and attack speedsters like Flash, to the degree where he can incapacitate entire Justice League. His physical strength and durability dwarf that of Superman, although he is slightly slower. He can alter his density and size, becoming intangible (which Darkseid can negate), and growing to the size of building. However, his most deadly power is his fire aura, which can put heat-immune Scorch to coma.
So, who would win in a fight?