Who's more Evil:
DARKSEID, He wants to enslave you and achieve the opposite of life, which is not DEATH but a miserable life as his complete and total drone/slave, for him death will be a release from suffering.
Who's willing to do anything to achieve there goals:
Thanos, will kill anyone or step over any one to achieve his goal, though Darkseid has even sacrifices Apokolips in DTONG and himself (countdow), but I still go with Thanos
Who's the better prep master:
I notice people say Thanos, but I am not sure, Darseid sacrificed himself in twice in order to achieve the ALE and release on earth in final crisis and most of things he does are planned, even his defeats are planned.
Who's committed the worst atrocities against the Multiverse:
This one is depending on the eye of the beholder. While Thanos has killed a lot of people, Darkseid wanted to mindless enslave the whole universe/multiverse, that is pretty shitty.
With all there gears and amps, who'll win in a fight:
I think Thanos takes this one.