I agree with your first choice, Grondy. All the other choices are plausible in this poll. But I think that each of those choices was able to be compensated for, thwarted, overcome, turned to good, and finally benefited all concerned. But in the case of Boromir, though he repented before he died, he did indeed die. The Company lost a member, and this was the only time they actually lost someone by death. Gandalf's death was not at all the same. There was no way that he would have been allowed to "leave" ME with his duty unfulfilled. Whether the intervention of Eru was necessary or not, he would have had to return because the demise of Sauron was his quest. (Even the first time I read LOTR, before I knew anything of Tolkien's underlying thoughts on this, I remember thinking "This can't be the end of Gandalf!") The death of Boromir alone, of all these choices, is the one thing that cannot be undone in the plot of the story. That is what makes it poignant. Hence, my choice remains the same.
And by the way, when are we going to be able to view the results of all those past polls? I have been able to see none save the very first. I want to see the others, too. Grep, when are you going to "fix" whatever it is, so that we can all enjoy those results?