Thanos. Unparalleled intelligence, great strategist, unbelievable strength, an elit in the field of telepathy, matter manipulation, energy projection, combat, and also historically successful in his plans.
Darkseid I don't see why anyone would want to be Thanos. Darkseid has a heck of a lot more going for him like being the God of Evil. Darkseid doesn't need an item of power to be a threat he's very existence is a threat to the multiverse.