Hard to put any moment at #1, I have 5 or so that are top for me.
1- Saving the raid on 25 OS 3D and getting us realm first.
2- Doing Naxx 40 for the first time
3- Killing KJ and watching my buddy going crazy because the legendary bow dropped and he was only hunter in raid(We raided at the same house)
4- Getting Rank 1 two seasons in a row with different partners
5- Raiding original ZA for the awesome Amani War Bears, then selling them x3 every 3 days.