For pure gameplay value, I still favor FD/GI. It was the first competitive deck that I built from scratch, and is still the deck I'm most comfortable playing.
For sheer LOL value, I've played a couple of fun ones...
There was a WP/DoD that grew out of helping a new player with their first deck. With Zunshen and Hehkeem in command, the deck had some interesting threats in a creature vs creature matchup. Zunshen himself was an amazing blocker, and turn 8 Hehkeem + Zunshen would wipe defense lines easily.
Verore/DoD was another interesting one, but not for the morale burn stuff. The reason I remember this is because the day of the Veroria change, this deck was made utilising Veroria and Jialan for an invincible (almost) fortress.