My best Whedonite memory is not a single moment, but pretty much watching both shows back to back for the first time (I watched BtVS when it first aired, but they were already halfway through season 4 when I was finally allowed to watch every week) with my flatmate during my last year in grad school.
It's not just the show, although I loved it of course, but it's also the brilliant memories of living with my best friend and uber geek, spending my days in the library and occasionally in class, then coming home exhausted and finding she had already prepared a TV-friendly supper, the menu music was playing and we'd watch and be totally absorbed until silly o'clock. Or she's be out and I'd attempt to cook (haha), and if she wasn't home by a certain time I'd text her and ask what time she'd be home to watch Buffy. We made thoroughly weird party guests throughout the entire year, because we were communicating almost exclusively via Whedon quotes and crack up all the time because something would remind us of a scene (there's a video of us doing the Dance of Joy at a birthday somewhere, banjoed out of our heads on Echo Falls rosè).
So, yeah. That pretty much covers it.. Of course there's many intrinsic moments of the show that I loved, but nothing beats the overall experience as a whole.