The most spectacular item I saw was comet Bennett in the early '70s.
At it's peak, it was right on the horizon just before dusk, it seemed the tail went halfway to the zenith. Extrordinarily immpressive.
OOps, dawn, not dusk...
I remember Bennett very well. At least I believe it was Bennett. It was probably the winter of 70-71. I was on a hunt in the Nevada desert, out where there was absolutely no light pollution at all. It was late or very early in the morning on a frigid cloudless night and I spied the comet in the west, the head low toward the horizon and the tail sweeping huge acrosss the sky. It startled me because I wasn't expecting to see a comet (I hadn't been following any news reports about it).
But I thought Hyakutake and Hale-Bopp were impressive, too. Had Hale-Bopp been as close as Hyakutake--that would have made for a memory of a millennium!