I personally don't like harnesses for walking, especially for dogs that don't know how to heel. You cannot really correct the behaviour, and harness encourages the dog to pull.
I do love prong collars for larger dogs, ONLY when they are used PROPERLY. When not used PROPERLY they are ineffective!
This is how they should be fitted:
http://leerburg.com/fit-prong.htm
If the collar slips down the neck, another link has to be taken out. In no way it should be used to hurt the dog or stop him from pulling, it is used to CORRECT! Which means you you don't let the dog pull while wearing a pron collar, but rather correct the unwanted behaviour by a sharp movement of the hand and relax the hand. There should never be tnetion on the leash. If the dog behaves, reward with treats and praise.
It looks intimidating and to some even cruel but it is a great training tool when used properly. It's purpose is to correct, not to punish, not to cause pain but to CORRECT.