Mine is Bert from Pyramid of the Sorcerer/Mystery of Mt Sinai. She was charming and likeable. And even Indys father couldn't cope with her! My second fave would have to be Alecia Dunstin.
If we’re including the comics in this, Sophie Hapgood. I love the character—Marion’s still my favorite Indy girl, but Sophie’s a close second—but don’t think she’s written especially well in either comic she appears in (I haven’t played the games).