Harnesses have differing functions and are designed for specific purposes so its important to choose wisely. Many people choose a harness because their dog pulls when on a leash and they want to avoid pressure on the dog’s neck. If this is the case for choosing a harness it is generally better to teach your dog to walk on a leash without pulling. Training Collars Choosing A Dog Collar
Broadly speaking harnesses can be placed in one of three categories.
Working - tracking, carting, drafting, freight pulls, guide dogs
Companion – walking, skijoring, running, urban mushing
Control (Restrictive - No Pull Harnesses) – Front-clip restrictive harnesses,
Not Recommended: Easy Walk, Freedom Harness, Sense-ation Harness, Sure-Fit Harness, Wonder Walker Body Halter, Walk Your Dog With Love Harness, DT Universal No-PUll Plus Harness, Comfort Flex
HOW TO CHOOSE A HARNESS
When selecting a harness choose a properly designed “Y” harness. The “Y” harness has “straps that fit tightly around each side of the dog’s neck, almost like a collar, and meet a third strap that runs under the dog's chest. (See fitting guide on right)The point at which the neck and chest meet forms a "Y" that sits right on the manubrium - the part of the sternum (chest bone) that is closest to the front of the dog.” The “Y” harness places the majority of the pressure from the harness “on the manubrium, which is a very stable bone that supports the entire dog's body.” The neck straps should be snug so they do not slip down and put pressure on the shoulders. “No part of the harness should “cross over the dog's shoulder blade (scapula) or upper arm (humerus)”. A properly designed and well-fitted harness does not have restrictive straps that sit on top the biceps and supraspinatus tendons. A harness should permit the dog’s legs to have full range of motion to extend forward and reach back unrestricted. The girth strap should be fitted about 2” behind the front legs so it’s not pushing into the elbows.
"Dogs with high shoulders should never work in harness. A harness bearing down and rubbing on high shoulders can cause intensely painful bone bruises." - Structure in Action by Pat Hastings and Wendy E. Wallace, DVM, cVA
You would not wear a poorly fitted jacket, backpack, safety harness, or shoes, so don’t subject your dog to an improper or poorly fitted harness.
For most dogs a collar is recommended. When choosing a working or companion harness choose a Y harness (non-restrictive) that is designed and fitted tightly around the neck so it doesn’t slide back and put pressure on the dog’s shoulders” altering your dog’s gait which can result in injury over time. 
   (M. Christine Zink, D.V.M., PH.D.)
No-Pull Restrictive Harness (Not recommended)
"No-pull” restrictive type of harness are potentially damaging to the front legs.
As a specialist in canine sports medicine Dr. M. Christine Zink* has significant concerns about the use of harnesses that wrap around the front of dog’s forelegs. (Whole Dog Journal May 2013) Dr. Chris Zink should be releasing her “limited gait analysis study” sometime in the near future which will address concerns with these types of harness.
Here is a great article on harnesses by Dr. Chris Zink. http://www.alpineoutfitters.net/scripts/article.asp?article=01
Harnesses We Use And Recommend
Urban Trail Harness - Alpine Outfitters
The Urban Trail Half Harness is perfect for use in a variety of dog activities in addition to mushing, such as scootering, bikejoring, roller blading, canicross, skijoring, tracking, and hiking. This harness works equally well for walks around the neighborhood. This harness extends only part way down the back to accommodate the steeper pull angle associated with biking and scootering.
Pulling pressure is on dog's chest, not neck and shoulder, and because it reaches half way down the back, it eliminates downward pressure a standard harness puts on dog's hindquarters.
Rotates freely around dog's torso, thereby helping to reduce "crabbing".
Good for big dogs
Great for senior dogs, easy on the hips.
Fully padded with premium quality Polartec Polar Fleece and is extremely lightweight, durable, and is machine washable. Contrary to appearance and perception, Polar Fleece does not readily absorb moisture; due to its hydrophobic nature, it only retains 1% of its weight in water.
Distance Harness - Howling Dog Alaska
The Howling Dog Alaska Distance Harness is the harness of choice for skijoring, bikejoring, canicross, scootering and dog trekking. It is an ideal harness for the use with BTL and Springer bike attachment.
This harness is one of the most popular harnesses for long distance mushing. amazon.com http://amzn.to/2CDdYRw
The Distance Harness only reaches about 1/3 down the dog's body, which eliminates the pressure on the dog's hips while pulling. Therefore it makes this harness an excellent choice of a harness for any dog with lower back problems. Crabbing dogs (dogs running sideways) will straighten out. Our harness comes highly recommended by Wes Rau, top canine physical therapist.
Blue-9 Balance Harness (non-restrictive). https://www.blue-9.com/pages/balance-harness/ The Blue-9 Balance Harness was appropriately designed taking canine anatomy into consideration. Fitted properly the harness neck straps fit around the neck so they do not slip and put pressure on the shoulders. The Balance Harness does not have restrictive straps that sit on top the biceps and supraspinatus tendons potentially damaging the front legs.
Blue-9 has a great guide for fitting for a harness. https://eshop-image-edge.sapanywhere.com/eshop/T9002251452416/uploads/2017/09/balance-harness-poster.pdf
The Mini is a comfortable pulling harness for small breeds. The Mini is a “little brother” to the Second Skin Harness by Howling Dog Alaska (Mini is constructed out of the same soft, breathable and quick drying mesh material). The Mini features reflective strips for increased night time visibility. The body strap is adjustable. https://howlingdogalaska.com/products/mini
Measure the neck circumference below the collar position.
XS: neck 9", chest 12” max" (3-4 lbs.), Chihuahua, baby Yorkie, baby Maltese
S: neck 10", chest 16" max (5-7 lbs.), Chihuahua, Yorkie, Maltese, Toy Poodle, Papillon, Pomeranian
M: neck 13", chest 18" max (8-12 lbs.), Shih Tzu, Boston Terrier, Miniature Dachshund, Miniature Pincher, Pekingese
L: neck 14", chest 25" max (13-19 lbs.), Fox Terrier, Beagle, Shih Tzu, Miniature Schnauzer, Pug, Boston Terrier
XL: neck 16", chest 28" max (20-30 lbs.), Cocker Spaniel, American Eskimo, French Bulldog
Car Safety Harnesses
The Kurgo Impact Dog HarnessTM is the next generation in Kurgo crash-tested car harnesses. Based on 8 years of engineering dog car harnesses, the Impact Harness is a totally new harness design using a single piece of high tensile tubular webbing with reinforced bar tacking. It is purpose built for car safety as well as your dog’s comfort which reflects all of the knowledge we have developed over the last 12 years developing pet travel products.
This harness has been tested at an established University testing facility using the Federal Motor Vehicle Safety Standard for child restraint systems. It has been tested with a 130 pound simulated dog.