Out of all the quests which ones made you feel warm and accomplished as The Courier? Could even be the small stuff, like returning a toy to a child. I'd say rescuing Joana from Gomorrah and reuniting her with Carlos in "Bye Bye Love", especially if you do so without asking for any sort of payment. After they leave Vegas, they gratefully and tell you that they'll never forget you and hope to run into you again. Also convincing Alice to reconcile with her parents and stay in "Someone to Watch Over me". Good karma, the gun, the reward, Alice and her mother both survive and they go back to daily life.