How should I hold a girl?

whatever is most comfortable. My husband is quite tall, so it's easier and more comfortable for him to put his arm around my shoulder

The waist is appropriate in most situations, I'd say.

I find waist more natural, less awkward...

Is she your girl? I'd suggest waist.

With your hands.

In your arms.

By the handles.

By the neck

I get to hold them anyway I want in the embalming room