Re: Collar or Harness
I've never used a harness for walking since I have trained my previous dogs, and now Pecan to pull in a harness.
I primarily use a standard O or D ring collar and as einspanner noted, the Mendota lead.
One thing to keep in mind with attempting to train a puppy to walk with a specific pace (that specific pace being your walking speed) is that when they are smaller, they have to generate a lot more pace with their short legs to keep up with your regular stride and then adjust their pace to a lower one as they grow into their adult form. So through their growing process, it takes a lot of adjustments to continually get them to slow their pace, let alone focus on you instead of their surroundings.
This was told to me 2 dogs ago and made a huge difference while walk training and that's to maintain your stride and pace at the most consistent rate possible as we have much longer legs. So small changes in our pace and stride length are much bigger changes for them to attempt to match with their pace and stride length. So if your stride/pace is consistent, it is much easier for them to understand what you are asking: to match your pace, and to keep their focus.