For me it's a toss up between PD II (Feb 2003) and December 2009. Both events I experienced in Philadelphia and Lancaster County, PA respectively.
PD II: I was in high school in Philly just got into winter weather tracking and had access to the Internet at my high school library for the last period of the day. The librarian was always gracious enough to let me just quietly geek out on model guidance and NWS web pages. Watching this storm get more and more interesting as we closed on the end of the work week was awesome.
December 2009: I was working 2nd into 3rd shift at the IT Help Desk at Millersville University and got paid to do homework and watch both the 18z and 00z model guidance come in on a triple monitor display with a nice Internet connection. I was also was a lead forecaster for our campus weather service at the time, and we had access to a read-only version of NWS chat. It was just pure giddiness to watch the 1.5" QPF line creep north with each model cycle, reach the AFDs from LWX/CTP/PHI and see the inklings of watches or warning start to come up in the chat rooms. I felt like I had access to almost secret data and it was AMAZING! Then came the morning before the event and I knew it was going to puke snow all along Mason-Dixon. It was the end of my undergraduate years and I was supposed to walk in graduation on the 19th, but I knew that wasn't going to happen. So I rushed back to Philly and boom...White Christmas.