The most satisfying? has to be a touch shot.
For me it's the side-spin drop shot* that spins off the court. I love seeing my opponent explode from behind the baseline sprinting aggressively to catch it only to stop at the service line when he realises that the ball is spinning away off to the side of the court.
* I try this shot 1-2 times a set, but i'm not always able to pull it off.
Disclaimer: I'm NOT a coach...
Real tennis: https://www.youtube.com/watch?v=yDqnkLJ9BtM