Given the options, I’m not sure how to vote. My morality* would be the same as it is now, which is…way too long a post for a thread about super powers, so here’s the ridiculously-oversimplified version: the source of morality is interaction between sentient individuals, and the moral rights possessed by a given individual are those that they extend to others.
One upshot of this is that I don’t think it’s immoral to kill someone who doesn’t believe that people have a right not to be killed. Being certain about this for any given person, of course, would require objective omniscience that nobody has. But, in cases where one has standing to make a judgment in the first place (i.e., knowledge of that person’s future intent to harm other individuals), then the potential kill-ee having indiscriminately murdered large numbers of people in the past is as convincing evidence as any.
So, to use a hypothetical handily provided by another poster, Super Der’s behavior would likely pass moral muster with me, provided that he didn’t act until he was convinced that A) the dictator in question had no regard for the value of human life, and B) that dictator was going to put deliberate exercise to that lack of regard in the future. (That latter requires knowledge of something specific, not just “well, he’s done it before.”)
That said…morality is the bare-bones baseline for not being evil. Far more commonly, day-to-day actions are governed by ethics*, which are the subset of rules for interactions that serve as the baseline for being a worthwhile human being as opposed to, say, a steaming pile of dogshit (which substance, you’ll note, is not evil, but still quite odious and generally undesirable). While it might not be immoral to kill a given person, it’s certainly unethical as hell if you have other options to prevent them from doing harm. (To illustrate on a smaller scale, it’s in no way immoral for me to routinely tell everyone I meet that their mother was a syphilitic cum dumpster. You can see where morality does not suffice as a boundary.)
Ethically, then, it’d depend on what I thought my options were. If I’m a Kryptonian or otherwise nigh-invincible demigod, I’m going to do my damnedest to end the threat with the minimum possible violence. If I’m, I dunno, Johnny Storm…where I can’t be reasonably certain of nonviolent success against an armed opponent, but immolation is likely to be effective…then I’ll just have to take it case by case. That sounds like the second or third poll option, except that I wouldn’t necessarily be limiting myself out of morality, and I don’t think it’s a nitpicky distinction.
Dang, that was still pretty long. Oh well, if you don’t want overanalysis, don’t ask morality questions, especially on this board. Or any questions at all, for that matter.
*ETA: I realize there are multiple accepted definitions for these terms. I’m using the ones I prefer by way of explanation. Feel free to mentally substitute as you like.