I bought a neat dent puller the other day. I used it on the driver's door. It has a cup about 5" in diameter, and a lever on the handle that you sqeeze up, to create the suction. I pulled and tapped the edge of the dent with a rubber mallet. It came out about 90 % and when I get the door apart, I will do the rest.
My top was caved in and I was able to pound it out. It is very heavy metal and I used a large heavy rubber mallot. It took a lot of work to get the metal back where it belonged.