What is the Giver's favorite memory?

The answer to this question can be found in chapter 16 of The Giver. Jonas actually asks what the Giver's favorite memory is, but then he quickly backpedals and says that the Giver doesn't have to give it to him yet. 

"What is your favorite?" Jonas asked the Giver. "You don't have to give it away yet," he added quickly. "Just tell me about it, so I can look forward to it, because I'll have to receive it when your job is done." 

The Giver responds by saying that he would be happy to share his favorite memory with Jonas. The memory that he shares is a memory of a family at Christmas time. The memory contains a fire in the fireplace, candles on the table, snow falling outside, and lights on a tree that is inside the house. Jonas finds that last detail a bit odd, but that doesn't stop him from thoroughly enjoying the general feeling of the entire memory. Jonas witnesses the family sitting together and enjoying the company. The Giver asks Jonas what he felt, and Jonas describes two specific things. He explains that he felt "warmth" and "family." Jonas also says that he experienced a third feeling that he can't quite describe. The Giver tells him that the feeling is love, and the concept is completely new to Jonas.

"I certainly liked the memory, though.  I can see why it's your favorite. I couldn't quite get the word for the whole feeling of it, the feeling that was so strong in the room." 
"Love," the Giver told him. 
Jonas repeated it. "Love." It was a word and concept new to him.