Gods and Demigods need not apply as they are a bit too hard to gauge their power level. For instance Doctor Manhattan from Watchmen is fairly omniscient (even if some of it can be blocked) and can be in multiple places at once, and hence qualifies as a demigod so he doesn't count for this discussion. Another example of a demigod would be Cthulu or any of the Old Ones. Anything that was born before time, or alters time and space, is generally considered a demigod.
Doctor Who would be a tough call, as really its the TARDIS that affects time and space, but he's kind of symbiotically attached to it...he might be considered a demigod. You could make a case either way.
I would go with Alucard, from Hellsing. He is their version of Count Dracula on steroids. Effectively immortal, none of the normal vampire weaknesses apply like sunlight, religious symbols, or stakes. He can regenerate and reform his entire body from a drop of blood (or reform from possibly nothing at all, its hard to tell, they never say out right, but considering he can live in a state of amorphousness and he's immortal...). He can shapeshift, even transform into a demon or amorphous darkness. It's hard to gauge how fast he is but he can traverse rooms in the blink of an eye. All this plus standard vampire tricks like hypnotism, telepathy, etc. He's also incredibly skilled and uses technology, expert marksmen, etc.
I think he could beat most versions of superman even without kryptonite
And even the insane supermans would be a draw, but with kryptonite he'd easily win.
His only
potential weakness is that Van Helsing somehow found a way to make Alucard work for the Helsing family. Yet he's clearly not enslaved. It's one of the mysteries of the series.