The down-side of the head halter is that you often need to train dogs to enjoy wearing them and, while some dogs automatically walk nicely with the head halter, other dogs and their owners require some training. Most owners who start their dogs correctly on one of these marvelous soft dog collars find that the relatively small time investment getting the dogs used to the collar is well worth it. For some dogs that time is only a few seconds to a minute of pairing the head collar with food. For other dogs I recommend a little practice every day for a week so that the owners are sure the dog loves shoving his nose into the halter on his own.
So there you have it, an overview of a variety of common collars and harnesses. None is perfect. They are all just tools. But some are more likely to cause problems in your pet or may just provide a less than ideal match for your needs. In case you're wondering which I prefer—ideally my dog can walk on leash with the flat collar he wears regularly. But for those dogs that tend to pull and need more work, I tend to recommend a front-attaching harness or a head collar of some sort.