The quick answer is to use whatever keeps your dog the safest. And, that will depend on your pet and your circumstances. Here are my favorites for different situations and conditions.
First let's talk about my favorite collar for the average size dog that doesn't pull, doesn't chew on a leash, and has a healthy neck and back. I love a martingale collar for the average easy going pet. A martingale collar is like a combination between a common flat collar with a safety extra. It has an extra loop that cinches in on the neck if the animal is pulling. This is critical because, unlike a regular common flat collar, if a dog pulls backwards while on a walk, there is no slack created. This is a classic move made by escape artist type dogs. If they pull back and do a quick snap of their heads, the collar won't slip over their heads like it will with a regular flat collar. I am not a fan of a regular flat collar for any dog for this reason. I have had way too many dogs try this move. My dog Betty can free herself from a flat collar in about 2 seconds flat.
For the little dog or older dog that pulls excessively, you may want to use something that won't put pressure on their tracheas, necks or backs (like dachshunds). For these dogs, you may want to use a harness. Harnesses can be tricky - especially for tiny dogs. Fit is very important. Small dogs can easily slip out of ill-fitting harnesses. Making sure that the harness fits perfectly is key here. A loose harness can slip right off of a little dog. Some great harnesses fit like a vest and have adjustable hook and loop closures with backup snap clips. These are harder to wriggle out of. I will link one below at the bottom of the post.
If you want a harness that deters pulling, a harness that clips at the dog's chest works for many dogs. There are several brands on the market. I tried one that is supposed to reduce pulling by making it uncomfortable on the dog when they pull by squeezing the shoulders and turning them around. These are meant as training tools. They are not designed as a substitute for training. If used over an extended period of time, some people think that they can allegedly cause joint problems so I do not recommend them for long term use. I do not know if this concern is valid or not but I didn't want to chance it with my own dog after I heard about the potential downside. Another option is a head harness that fits over the muzzle and clips under the chin. This is what I use on my own dog. The only downside to the head harness is it will leave an indentation in the fur on the dog's muzzle. For fluffy dogs, this can be unsightly. But, they really curb pulling.
What about big strong dogs that pull? Training is going to be your best friend with big dogs. If you have tried harnesses and headgear that is not working and safety is an issue, because you have a big strong dog that pulls excessively, there are times when a prong collar can be a game changer. HOWEVER, you need to know how to fit it. You have to know how to use it. AND, you have to train your dog to use it. If you use a prong collar, you need to also use a choke collar as backup because prong collars can break at the links. This collar can be a very useful tool after you have tried the softer collars. The prongs squeeze in on the dog's neck when it pulls. I have several client dogs that need prong collars for different reasons. Some are very strong and pull excessively. Without this collar, they could not be walked safely in the city. Others are very reactive to other dogs and people. Again, the collar allows them to be safely walked. When you work with rescue dogs, some have been abused and have some reactions that take time to rehabilitate. Some are wonderful at home but are never really great out in town. These collars make control and safety possible. So, if you see someone using this collar, don't assume that they are abusing their animal with a severe and uncomfortable collar. These collars get bad press from the positive reinforcement camp. However, after working with trainers and the dogs that have benefitted from the use of these collars, I will not rule them out.
So what about leashes?
Let me say this... I hate retractable leashes. They can snap unexpectedly. If they are weak at the connection where it is hidden in the hideous plastic box that it winds up into. I hate the bulky handle. Good luck walking more than one dog comfortably and safely with those handles. I always walk with the leashes in one hand and leave my other hand free for directing dogs closer and directing their movement and scooping poo. This can't be done easily with a retractable leash. You also can't act quickly with a retractable leash. Just say no to these awful contraptions. They are not safe.
If you have a puppy or older dog that is chewing on the leash, a metal link leash is the best option. Dogs can chew through a leash very quickly. My Labrador Nikki that I had years ago chewed through several leashes when she was a puppy before I figured this out. She could chew a leash into two pieces in a few good bites. She was gifted like that.
Small dogs that are close to the ground need a little bit longer leash. The taller you are, the longer the leash needs to be also. A 6' leash is about perfect for shorties. A 4' leash can be a little on the tight side. With a taller dog anything from 4-6' is a great choice.
Training leashes can be longer (up to 50') Don't use these for walks though. You need to keep your dog closer when walking around other people. Training leashes are great for teaching recall, stays, and other obedience commands - but not for the average walk in the park or around the block. Longer leads are not allowed in many hiking areas. Many have a 6' max.
A padded handle is nice but I am happy with a regular webbed leash that can fit over my wrist. The padded handles seem to wear out more quickly. If you choose a webbed leash, double check the stitching every time you use it. Always inspect your equipment for safe usage before heading out. I don't buy leather because I am vegan and don't use animal skin.
Always watch for wear on leashes before heading out. If a leash is starting to tear, do not use it. A strong jerk can turn into a tragedy very quickly. I like to keep a couple of spare leashes in my car.
The spare leashes in my car are usually slip leads (I need to order a couple more at the moment). They are a really handy backup leash because they act as both collar and leash. I have given away several slip leads to clients that had excessively worn and unsafe leashes, harnesses that didn’t fit safely, and flat collars that slipped over the dog’s head. While I always prefer to use the clients equipment, if it is unsafe, I do carry backup leashes and collars in my car for emergencies. Slip leads are used by rescue groups and groomers because they are inexpensive and fit any dog safely. A slip lead is really handy for when you come across a stray dog too because you don't need a collar and you don't have to touch the dog as much as with a clip leash. These also come in handy if your dog's collar breaks. You can carefully slip the loop over a dog's head. Use common sense when trying this with a dog that you do not know. If the dog is snarling or growling at you, call animal control and keep a safe distance. Never try to handle a stray dog that has been injured unless you have experience doing this. Call for help. But, if the stray is otherwise healthy, friendly and just a little timid because you're a stranger, a slip lead is a good choice. You will usually only get one chance though. Proceed with caution with stray dogs though. This is just what I do. Helping strays is always at your own risk.
If your dog has been injured or becomes sick, keep a muzzle that fits your dog at home and in your car as well so you can handle them safely. You will need to muzzle a dog that has been injured before trying to handle them. However, never muzzle an unconscious dog or a dog that is having trouble breathing or is vomiting. A leash can be used as a muzzle in emergency situations once your learn how to wrap it around their muzzle and secure behind their ears. First aid and pet CPR classes teach this method and are very useful for all pet owners. They even have online courses available now that are very inexpensive. I prefer a live classroom course for at least the first time. But, the online versions are great to use as refresher courses.
I hope this is helpful to you when selecting safe equipment for your dog. If you have found this helpful, please feel free to share with your friends.