Each person will experience a moment they want to freeze and preserve for all eternity. For some, it was some personal triumph: graduation, winning a sports championship, completing one's life's work. For others, it was something more intimate: a first kiss, birth of a child, a treasured family memory.
For Harry, it was the moment he saw his soon-to-be wife Daphne at the end of the aisle, looking positively angelic in her wedding dress. The smile she gave him as their eyes met was equal parts joyous, sheepish, with a slight undertone of mischief at the reaction she'd elicited from her soon-to-be husband.
This was their triumph. Their relationship hadn't been easy with all the judgement they'd endured due to the slightly forbidden/frowned upon nature of a relationship between the rival houses of Gryffindor and Slytherin.
Harry was possibly the most hated person for most of Slytherin house and otherwise generally disliked by the less extreme members of the house.
Daphne wasn't all that well received among the Gryffindor populace either, as her pureblood roots and association with the 'house of Dark Wizards' as it were did not help her case to begin with. The fact that any interaction a Gryffindor had had with her before she and Harry had gotten together was met with cold indifference on her behalf, her rather condescending behaviour rubbing them the wrong way.
Their relationship had been one of mutual improvement, as Harry's likeability and warmer personality had thawed away at Daphne's colder disposition, which had in turn won over her critics among Harry's house. Harry on the other hand, did begin to exhibit more of the Slytherin qualities the Sorting Hat had seen in him all those years ago. The damage had already been done, however and Harry was irredeemable in the eyes of Slytherin house.
Any fear of ostracizing was swept away once graduation came about, as any notion of house loyalty dispersed as all the students went about starting their adult lives.
The stars seemed to shine on Daphne and Harry, as they both wound up with Ministry jobs, Harry being immediately accepted into the Auror Corps and Daphne getting a job in the Department for Magical Law Enforcement, meaning the two would work quite closely together.
Many lunch dates, dinners and a few holiday retreats later, and Harry finally proposed to her, to which she had tearfully accepted. That certainly came as a close second for Harry's favourite memory.
At this very moment, though, Harry was the happiest he'd ever felt in his entire life. He felt that, armed with this memory, he could take on all the Dementors of Azkaban with his patronus.
As Daphne reached the altar, she was handed off to Harry by her father, and the couple took each other's hands and gazed into each other's eyes lovingly as they prepared to commit the rest of their lives to each other.
"Do you, Harry James Potter, take Daphne Evelyn Greengrass to be your lawfully wedded wife? Do you promise to love her, comfort her, honor and keep her for better or worse, for richer or poorer, in sickness and health, and forsaking all others, be faithful only to her, for as long as you both shall live?"
"I do."