The happiest moment in my life was after leaving confession one day with then Father David, which includes getting married, having a kid, and even meeting the pope.
I was going through a severe depression that lasted around 9 months, and no matter what I did (which included more than a few sins), I just could not get out of this funk. I randomly decided to go to confession towards the end the school year, and in 10 minutes, I just remember leaving there like I had a great burden lifted from my shoulders. I remember walking by Sully on my way back to the dorm and feeling happy for the first time and almost a year. This is coming from a pretty unemotional guy.
I believe that the Holy Spirit truly was working through him. I do not know where my life would be right now had I not gone to confession with him on that day. Outside of baptism, which I don't remember, I consider this to be the most important day in my Christian life.