Great fanartz, Glaurung!
Other than that, I was going to vote for Aeris' death (yes, I refuse to use the term "Aerith" whenever I remember it. Also, I'm sure Glaurung will know one of the reasons why I do this!) but, after I thought about the whole compilation stuff, I have to change my opinion.
Zack's Death is actually the most memorable point of the Compilation, for me. It's the starting point, as it has been mentioned already, the reason everything happens. It means a lot more to the General Compilation than the death of Aeris does.
If I was to choose a moment of FFVII alone, I would choose Aeris' death, because, while Zack's death appears there too, it bears not the same meaning. I mean, to me, Zack's death is memorable BECAUSE of what we see in CC, etc.
I know it's a bit of a stupid way of thinking, the fact that the same two scenes would be rated differently if I say "Compilation of FFVII" or "Just the original FFVII", but it's the way I think...
Damn, that made no sense at all!