Nothing better than digging eight fingers in (some people are all thumbs---I'm the complete opposite.) I like to alternate from the front and the back.
From the front, the advantages are being able to see into her eyes, as well as see her stomach, which is always a turn-on for me, but the way the fingers curve, this doesn't always bring the most intense tickling.
From the back, the story is just the opposite. The natural curve of the fingers allow me to really go to town, and create the most intense reactions, but I can't see what I want to see.
Oh wait, did someone say get a mirror?