Hand Holding
Disclaimer: I don't own Avatar: the Last Airbender
Aang liked holding hands the best. Sure kissing was nice (tongue clashing whistle you swapped DNA with your partner) and sex was definitely great (more DNA swapping). However, hand holding was Aang's favorite part of a relationship.
Two pulses beating together under a thin layer of skin. Fingers intertwined as if they were little bodies making love. But the best part with hand holding was soul. Every time you gave up your hand you gave part of your soul to the other person to hold for the time being and vice versa. It wasn't until you or the other person let go that you would get that part of your soul back.
That's why hand holding was Aang's favorite part of any relationship and it was important for him to hold Katara's as much as possible.