First let's address the point of the costume. Bubonicus - cheap ripoff of a Sentinel. Mordru - basic medieval. If tunics are skirts I guess Robin Hood wore a dress too. As for the hats, well, yet again Bub's helmet screams Sentinel whereas Mordru's screams crazy man. I mean seriously, who but a crazy person would sport that hat? I don't know about you, but I'd be more afraid of a crazy near omnipotent sorcerer than a Sentinel with a wand. As for the evil quotient, be patient, we'll get to that in a bit.
Let's talk about Mordru's orgin story for a moment. In Adventure Comics #369 Mordru the Merciless escapes imprisonment. Shadow Lass, a new addition to the Legion, is told the story of Mordru's rise and fall. We learn that Mordru was a powerful sorcerer from Zerox (later known as Sorcerer's world) who mastered "ultimate mystic powers" that allowed him to take control of his own world. After consolidating power on his home world he engaged the rest of the galaxy in open warfare - and the war only stopped when he decided that he had conquered enough worlds for the time being. After many years of quiet from Mordru's domain no one expected the next attack. "Mordru went where he wished... conquered what he desired. Sometimes he sent his armies, sometimes he himself took what he wanted."
As near as I can tell Bub has no orgin story. The most we get is that he believes that life is a disease and death is the cure. Gee, that's original.
Now I'd like to talk about powers.
Mordru is a being of near omnipotent magical powers - which means he can even take on heroes such as Superboy and Mon'el. Even having his own powers reflected back on him (see LSH #48 during the Giffen years) only serves to momentarily stun him.
Bubonicus has a wand and some armor. His wand makes people sick (some sort of tech that mimics Infectious Lass' powers near as I can tell - and she was only a member of the Substitute Legion) and his armor is... well, armor. Oh yeah, he can also live a really long time. Oh yeah, and survive in space - grats Bub, so can Dawnstar.
Hmm, I'm thinking that on power scale alone Mordru would make Bubonicus curl into a ball and cry like a little kid.
Now let's move onto the "evil quotient". Let's talk about Bubonicus first. Lee pointed out that he was listed as a "cosmic eradicator". Well that's sweet and all, but what does it really mean? As far as I can tell Bubonicus' evil originates from the fact that he infects people with seemingly incurable diseases (yet again, Infectious Lass on a more cosmic scale) and leaves them to die. Yes, that's pretty evil, but it's impersonal. Bubonicus kills with a detached purpose, and while horrible in it's result, it lacks that true moral depravity. In all actuality Bubonicus seems so removed from the creatures it infects that it doesn't seem to understand or care about the suffering it causes.
Mordru, on the other hand, knows exactly what kind of suffering he causes - indeed, he thrives on it. Not only did he start out as a mystical Hitler, but as he grew older he became even more depraved. During a period of supposed "reform" he married Mysa Nal aka White Witch. After having his powers returned to him he swiftly reclaimed a position of power, declaring himself Emperor of Tharn (the second incarnation of Sorcerer's World). He imprisoned and tortured Mysa although she was eventually rescued by her friends.
chaining your wife to the floor and summoning spiders... evil
beating your wife, also evil
burying your wife alive, really frelling evil
If that wasn't awful enough he then manipulated Mysa into giving into her hatred so he could absorb not only her power - but her essence as well. He then used that power to raise the dead. And if assaulting the known galaxy with undead wasn't evil enough, he also raised the Legion's own honored dead to fight against them.
note: check out zombie Reflecto! now that's just funny!
Making you fight your dead little brother, definitely evil
Mordru was evil in every sense of the word, not only in the impersonal dictator who perhaps somehow justifies his actions - but also on a personal level. Mordru was a man who only found joy in bringing suffering and pain to others.
If we're talking about an evil quotient I think Mordru wins the evil pageant hands down every time when Bubonicus is the competition. In the end though, a picture is worth 1,000 words:
Thank you folks, and goodnight!