One of the reasons I really like the Superman villain, The Parasite, is because of the variety of abilities at his disposal.
He can drain energy so quickly that normal humans (and even some pretty decently powered metahumans) are instantly turned to dust when they get within a few feet of him, if he chooses. Superman and other higher-tier heroes only last so long against him because they have more energy to spare. Of course, that fact changes the longer the fight goes on. He can also drain energy through a psychic link, so if someone were to attack him telepathically, it would be almost as much a suicide as outright shaking his hand. The energy he absorbs doesn't even have to be life energy; it could be kinetic (stopping something that's been thrown at him in mid-air), heat (Superman's heat vision), electricity, and nuclear energy.
Of course, if he drains all of the life energy from a metahuman, he of course gains their powers for what could possibly be a few days, unless he goes absolutely nuts and splurges it all at once, which would probably reduce that time substantially.
He's also psychic, able to learn whatever his victims know. This knowledge doesn't fade away like the physical energy he absorbs; the knowledge and memories are retained in the Parasite's mind permanently. He can also incorporate victims' behavioral patterns into himself, which comes in handy whenever he's impersonating someone, which he does using his...
...Shapeshifting ability. Referred to as "the perfect duplicate," the Parasite could alter his cellular structure to become someone else, right down to their DNA. The only limitation to this is the fact that he has to drain the impersonee once every 24 hours in order to maintain the disguise.
His own brute strength (without having drained superstrength from anyone else) isn't anything to scoff at either. While it's probably not anywhere near the level of Superman or the Hulk, he's still been shown effortlessly smashing his way through pavement, steel, brick, surviving the vacuum of space, and other dangerous environmental circumstances requiring much increased physical strength. His physical strength is balanced by the Parasite's second personality, Doctor Torval Freeman, who provides strategy and battle tactics to the Parasite's dominant personality, Rudy Jones (a guy who probably didn't even finish high school).
The Parasite's also shown able to heal from such grievous wounds as being burned to his skeleton, provided he has energy to fuel the healing process.
And unless we count the new story going on in the Superman titles (I certainly don't), Parasite has shown no limits to the amount of energy that he can take into himself, once even reducing Superman himself to a frail husk, barely able to bring himself to lift his own arms. And Rudy showed no ill effects from draining so much energy from Superman, let alone any signs of having a 'full stomach.'