I've had a couple due to Gengar that were a lot of fun, however the most exciting game I've ever played was the BR I won against the current reigning world champ. It was the fourth BR in a row that we were top 2. We were both playing the same decks(Machamp for Steve, Blaze/BlazeFB/LuxrayGL for me), but I switched out 3 or 4 cards for better choices and took 6 prizes two games in a row. Steve and I both had a blast and were laughing the whole time.
I didn't play another BR, and then didn't do too well in cities due to poor deck choices (Darkrai + Cresselia at the GA marathon? What was I thinking?), but all through the marathon in GA a lot of people were playing Gengar. I ended up activating feinting spell a few times to take games to sudden death. One particular game I had the warp point in my hand to get around feinting spell and forgot about it. That was the most stressful sudden death I've ever played.