most powerful superman villian

[Adekis]

I've always been a fan of Metallo. A guy who's not far from Superman in the strength department, and maybe even gains an advantage in the Kryptonite factor. My favorite Metallo is probably the one from Superman / Batman Public enemies...

I also love Brainiac, especially the Bronze Age one, the totally pure evil robot one. He was pretty great. Not that I don't like other Brainiacs, he's just my favorite.

Superman is a hard guy to come up with enemies for. Some of my favorites are just gangsters, Golden Age or Intergang, or anything in between.

He is supposed to fight crime, not just super-terrorists and extra-dimensional monsters.

[Meach]

Well, I guess "realistic" leaves out Composite Superman. 

How about Mongul? 

I also always thought that Faora was quite a scary and formidable villian, given her hatred of men, her obedience to Zod, and most importantly, her knowledge of Horo-Kanu. 

[Permanus]

I always enjoyed Alan Moore's version of Bizarro, who realised that he had to kill himself since Superman is alive. Last words: "Hello, Superman. Hello."

As for the most powerful Superman villain, well, I would have thought that General Zod and his lot had pretty much cornered the market. Or Vartox, who wasn't exactly a villain, but was fantastic and why isn't he around any more? Oddly enough, I rather liked the John Byrne revamp of Luthor as the Kingpin because it made a lot of sense: here was someone Superman couldn't do anything about because his power was that of a man behind a big desk.

[DBN]

The most powerful Superman villains would be a creative and editorial team that doesn't understand the character.

[superboy]

Heh Heh.Touche