People are often shocked by my answer. Simply put, I want a nice fitting harness with both front & back clips and the longest leash that is safe for the environment we are in.
The Pet safe 3-in-1 is my preferred harness for adolescents who always struggle with impulse control. However they are pricey so not always best for rapidly growing puppies. A solid Y-front harness with a back clip that sits behind the shoulders is almost always acceptable. More crowded places require shorter leashes and less crowded places allow for nice longlines for safety.
Any tool designed to cause pain, restrict body movement or remove breathing is a HARD NO in my book.
Why I walked a dog on a slip lead a few nights ago.
Clients come into their first session with dogs wearing all sorts of unsafe gear. It's NOT their fault for believing advertising on the package or following the advice of same trainer they saw on TV or somewhere online. There are so many available options that it's nearly impossible to navigate the choices without help.
The dog a few nights ago came in a slip collar, which was designed to cut off a dog's oxygen if they pulled in an attempt to force a dog to walk with their human. I always try to switch unsafe gear out for safe gear at the beginning of the session. This dog was gear shy and already afraid of the harness previously used on the dog with previous owners. We help most of the session off leash as most first sessions are anyway. But the dog needed to go potty. So the choice became take the dog out on the gear they were used to or ignore his attempts at telling us he needed to go. We chose to take the dog out to potty in nearby grass.
Here is the dilemma!
My clients know I don't use these tools so seeing me use them can create controversy. Especially if this is discussed on social media sites that are often quick to condeem or point fingers.
In a perfect world, I would never in a million years choose to use any tool on a dog that was designed to cause pain. No dog deserves to be trained that way.
We don't live in a perfect world! Sometimes we need to choose between two bad choices because a 3rd more acceptable choice isn't an option.
Had I told this client that their dog couldn't go out to potty because of a bad tool, that client may have felt like I was unfairly judging them and/or their dog. That client may have left that first session and never came back feeling too ashamed. Instead I shared kindness, awareness, knowledge, and empathy (CAKE) with the client. We created a plan to help desensitize the dog to a different style harness as well as a plan to work on the issues the client came in to address.
Awareness: letting the client know that their concerns are valid and important to me.
Knowledge: info about what science tells us about the situation the human and dog are in. In this case, information about gear.
Empathy: letting the client know that I've experienced challenges in the past as well and I will help them as much as possible.
CAKE!
Everyone deserves CAKE!
Thanks Andrew Hale for teaching this dog trainers, behavior consultants and dog owners around the world through Dog Centered Care!
Dog Centered Care on YouTube 
