Having tried various options over the years, from flat collars to Halti headcollars, to Gentle Leaders to various harnesses, I have found the Perfect Fit harness with the front clip the best.
As I see it, even the best behaved pups are going to pull while they are learning, even if it’s just the occasional leap towards something that takes their attention momentarily. I would prefer to avoid any trauma to the neck in that situation and by using a well-fitted, fleece-lined Y-front harness with a D-ring at the front as well as on the back, you are able to control them with no pressure on the neck.
The front D-ring basically means that if they do pull they turn themselves back to face you, then as soon as they’re back with you, you can reward and remind them that that’s the fun and rewarding place to be.
I wish they had been around when I lead trained my Border Collie x Belgian Shepherd (a very looong time ago) as she was the most challenging dog I have ever had to teach to walk to heel. Back then I just used a flat collar and she did get there eventually, but it took A LOT of time, effort and determination. She was the dog a trainer recommended the Halti for - nightmare - never again, she hated it with a vengeance and it set us back weeks in our training.
Once my dogs are well trained and able to walk to heel I will use just their collar occasionally. For example, I wouldn’t bother putting a harness on just to take them to get in the car and I tend not to use them at the vets, as they can get in the way, depending on what the appointment is for. I make sure I do lead training on the collar as well, so that if I ever need to get a lead on them in a hurry I can do so without needing to get their harness on first.
Perfect Fit Harness