Re. Jesus' sacrifice. Have has some very interesting exchanges with William Hawthorne (who is an excellent contributor) that are worth posting, I think. I'll give my response to William shortly. For an additional comment by William, see comments on Jesus sacrifice.
The issue is vastly more complicated than you make it look. At least one important factor you left out is that Jesus experienced God's wrath (or so the Christians would tell you). From within the Christian framework, then, this would be nobler than any earthly death you care to pick.
Tweaking your simplistic cases to include this detail, we get something like:
1*. Bert is convinced he can save all mankind from eternal damnation if he is prepared not only to die horribly, but to have the wrath of a perfectly just God poured out upon him, after which he will be resurrected. He makes the sacrifice.
2. Tim is convinced he can save the lives of several individuals (perhaps his own family) if he is prepared to die rather horribly, period. Tim being an atheist, supposes death is final. He makes the sacrifice.
Once we include details like this (and possibly others), your claim that most of us would do what Jesus did is implausible (or at least, inscrutable).
Thanks for comment. Do keep contributing please as these are interesting remarks.
I shall respond to your comment in a main post but first can you clarify something:
(i) why is it necessary that Jesus face "God's wrath"? (ii) what does facing God's wrath involve? (iii) does he face it before or after his bodily death? (iv) where is the evidence to support the view that Jesus faced "God's wrath"? I can't find any in Bible, other than maybe his final "forsaken me" comment (which, I seem to remember, Plantinga takes to be such evidence - do you?).
Also, what are the other "important factors" to which you allude? Let's get them all on the table...
I don’t know the answers to those questions. And I think even if I could suggest possible answers, they’d be theologically controversial at best. But the fact that you implicitly concede that you don’t know what God’s wrath involves, or whether Jesus even endured God’s wrath, only serves to underscore my point: your claim that most of us would do what Jesus did is implausible (or inscrutable). You're realize, I hope, that a philosophically careful comparison of the nobility of deaths in (1) and (2) would require, for the sake of the thought experiment, that we suppose the Christian framework is legitimate. And once we do that, we’re left with all sorts of possible details to consider. Some of them we might not even be able to make sense of, and some might in principle be unknowable.
If you really want to show decisively that Jesus’ death was less noble than the atheist’s, you’d be forced (awkwardly, given your atheism) to put on the theologian’s gown and wrestle with a variety of nuanced theological interpretations of Christ’s work, all of which will have a bearing on your intuitions when judging the two deaths. For an example of just one interpretation, many theologians believe Christ went to Hell after he died, and was saved by God (Himself) thereafter. What’s easier to face: nothingness, or a temporary stay in Hell? Seen in this light, I doubt many people could confidently claim that they’d do what Christ did. And it won't do to respond by asking what Hell involves, and why it was necessary that Christ vacationed there. For if we don't know the answers to those questions, we have even less of a basis to justifiably assert that most of us would do what Jesus did, much less that an atheist’s death is nobler than Jesus’.