Girls, until the age of roughly 22-24, need their necks supported at all times. For they do not yet possess the necessary muscles and motor skills to keep their head upright. Thus, It is imperative that girls be held in such a way that cradles the neck.
In addition, a girl's skull, more specifically her fontanelle or "soft spot" is still vulnerable and not fully sealed up until approximately age 37 (sometimes more developed females can have cranial closure by 32 , but this is fairly uncommon). As such, be very mindful when holding a girl that kissing her on the baby spot can split her skull wide open.
Aside from that, there is no "best" way. Girls, women, people, like to be held in different ways over the course of their day or lives. Romantic holding can be smothering-tight or gentle. A tight hug is sometimes the tits, but other times a mellow arm wrap around the waist is best at an outdoor concert or ocean gazing. When we are angry sometimes we want to be left alone; when we are in grief sometimes we want to be touched; sometimes we repel a gentle hand on our back.
Read cues, ask yourself what might fit best and trust your holding gut.
Lol, no but really, guys everywhere reading this, pay close attention to the neck. We will love you for it!
Make sure she's the right way up too.
Hint: the feet go on the ground.
Amit is right, trust your "holding gut". A woman can feel if you're being sincere in your gesture of holding her. Just hold her like you mean it. She'll melt in your arms!