I voted for PD1 - 1979. I was in northern Calvert, which was the bullseye for that storm. I don't know what the actual accum was with the extreme drifting, but DCA I think was 19" and the amounts were much heavier by the Bay so say 30-35". The wind was UNBELIEVABLE, like 40 mph with gusts to 60. It was like a hurricane of snow with howling winds and such whiteout that the woods just 75 feet behind the house were completely obscured at times. One observer in the area later reported 6" in one hour that morning.
My mother and her friend who was stuck with us tried to walk the 100 feet to where the cars were and actually got disoriented. They were legit scared when they got back saying that they almost got literally lost in the front damn yard! My mom said it was hard to breathe with the snow and winds so extreme.
When it was over, cars were only lumps in the snow and we had 6-7 foot drifts. One funny story is when my dad finally got his '74 Charger dug out, it would not start. He opened the hood and found the whole engine compartment completely packed tight with snow.
I have of course seen some great storms in Germantown since 1995, but NOTHING for me can top the Great White Hurricane of 1979.