Beings I do not support the use of choke, prong, and shock collars- it's important to know what IS safe to use as a training aid for your dog. There are a few different types of walking aids when training your dog to walk on a loose leash, I have found the BEST harness to be the Balance Harness.
The Balance Harness is different because it will fit ALL breeds comfortably. I have a Pit Bull type dog who has a broad chest, every harness I purchased for him didn't fit him properly causing irritation in the arm pit areas. I purchased a Balance Harness for my dog, Quincy and it fit him exactly as I needed it to. Quincy is a puller, I've been training him to walk properly on a leash while using the Balance Harness and I've seen such an improvement. Every strap on the Balance Harness is adjustable and doesn't dig into the dogs body. It's a comfortable fit to say the least. I like this harness because it has a clip on the back and on the chest straps of the harness making it have two points of contact when walking your dog, with a double clipped leash you can attach the leash to both points of contact on the harness. Also, this harness is designed to not rest on the dogs neck, this feature prevents injuries in the throat area and overall discomfort to your dog. If you have a dog that pulls, I highly suggest you look into purchasing this harness. The Balance Harness is a Seattle product designed by Lori Stevens and Dolan's Dog Doodads, LLC.
I've attached a link that will direct you to the Balance Harness website where you can learn more about this product as well as purchase a harness.