From Halopedia, the Halo wiki
Sycamore High School, University of Cincinnati
There are so many to choose from, but I'd have to say for gameplay my favorite moment is the Truth and level, and for a plot point, the first encounter between the Master Chief and the Ur-Didact in Halo 4.
My worst Halo moment was the Cortana level in Halo 3 on Legendary. That took forever to complete.
I've always loved Halo. It was the first real game I have ever played and it is the reason I got into video games in the first place. I got an Xbox and a copy of Halo for Christmas the year it came out, and I was only five years old.