I agree that prongs have their place in training and work remarkably well when used correctly on the right dog. That said, I don't feel a prong is for you, at least not yet. There's far more positive and mutually rewarding games you can play while walking to improve his focus on you and improve the loose leash walking. They don't work overnight, but they work in the long-term.
I'm lucky in that my dog was never a hardcore puller, but in adolescence he definitely had times where he would pull me to get to something good, pull when he saw another dog, pulled when he saw a shiny thing, etc etc.
What worked for me was a combination of several techniques used together. I used an Easy Walk harness for a spell (the front-attaching no-pull harness folks keep mentioning) which was VERY beneficial, and rewarded him positively when he kept the leash loose on that harness. I used treats, I used a friendly voice, I would pick up my walking pace excitedly... like Dekka said, life rewards. If he pulled in the EW harness, he got turned around, and didn't get anywhere, so it was a good start to teaching him what he was supposed to do, as opposed to simply what NOT to do like a prong.
When "weaning" him back onto regular harness and collar walking, I used a combo of things:
- "be a tree" when he pulled. When he pulled, I halted in my tracks. If we started walking and he pulled again, I'd halt immediately. He would get frustrated (and so would I, sometimes) but I was consistent.
- when he walked loosely, I would give positive happy voice praise and give periodic treats for walking loosely. The treats would be random, a sort of bio-feedback for doing what I like him to do.
- the Look At That game. This works especially well for distractions like people, other dogs, whatever. Use a clicker or your voice to mark. Before trying this on walks, teach him to make eye contact with you to a command of "Look at That. Click/mark and praise handsomely when he does, and build it up to the point of having him immediately look at you for the command. Then start using it on walks at random times, and build on that so that when distractions appear, he knows that he can look at the distraction, but that looking at you = a yummy treat and happy owner! Finn and I have brought the LAT game out once again since he's he's been having focus issues, and so far I've seen some great improvement.
Hope that helps some!