[SixOfSpades]

I like the pentagon formation myself--My best Tank on point, 2 backup Tanks in the other 2 forward positions, my weakest guy in the middle, and archers in back.

I also saw a screenshot a while ago--this person was using the V formation, with 2 Tanks in front (the corner of the V), archers and priests on the left wing, and Mages on the right wing. Of course, you're doomed if anyone attacks you from the right flank, but if you clear maps the way I do (Working your way around the outside edge, then spiraling in towards the center), all your attacks will come from the front, or from your protected flank. Not bad.