There are a number of articles that suggest that a harness is better than a collar. These articles suggest that harnesses disperses pressure over a larger area of the body. That is of course true. However what they don't do is discourage pulling or tugging. They just make it more comfortable, assuming that the harness is correctly fitted and the right size. Whether the harness is attached on the chest or the shoulder blades makes no difference, albeit for small breeds there is some evidence that back attaching harness are preferable since they can be more sensitive to front attaching harnesses. The problem is harness don't teach your dog anything. Like the numerous options of bits for a horse's bridal, there are numerous types of collars and all have a different function related to training.
Leather Roll Collar
For Norwich Terriers we recommend a rolled leather collar for everyday wear. A properly fitted collar allows you to slide two fingers under it, between the dog's neck and the collar. Of course the collar should not be able to be pulled off without undoing it. This collar potentially has some sort of identification tags for your dog (name and telephone number). While you certainly can use this for walking the dog, it is not a training collar.
Training collars are worn for the specific purpose of training. They should not be left on when you are not training. All collars need to be appropriately adjusted to function and fit properly. The simplest of training collars is the Martingale.
Many people find that once the training is learned, dogs walk at the heal position more comfortably ... and you may not need this collar at some point!