Please excuse Wylie's poker face in this article, he was not happy with me for waking him up from his nap 
Collars
Buckle collars are for tags and walking dogs that do not pull. The buckle is normally made of plastic and metal and is great for a quick release. They are also good for dogs that play and can get their teeth stuck in collars so long as there is a supervisor, if there isn't then use a daycare collar or no collar at all.
Belt collars are for tags and for walking, they are not good for playing dogs as they are difficult to remove and therefore can be dangerous. However they are good for dogs that walk loose-leash without corrections needed and who can break buckles.
Daycare collars are quick release collars with velcro or a snap off buckle attachment that hold the dog's tags and breakaway if anything gets caught. I use these for puppies and in daycares, they should never be used for walking.
Martingale collars (two kinds)
Martingale webbing collars are for dogs that slip their collars with ease. They are meant to be loose fitting but when tightened fully they tighten just enough to keep the collar from slipping over the dog's head. These are NOT meant for training, they do not have the same effect as a chain martingale collar or a choke chain. They are not for dogs who pull. I see lots of dogs wearing them with owners who think that they are going to stop pulling, that's not what they're for.
Martingale chain collars ARE for training, they were originally meant to keep the collar from slipping over the dog's head, same as the webbing martingales, but they actually now fit snugly, then the collar is used as a snap correction without tightening fully as a choke chain would. These collars do not fit loosely. They are use for training and are good for dogs that pull moderately or just need a quick correction here and there. They are not for extreme pullers, contrary to popular belief they can cause just as much damage as a choke chain.
Sledding collars or half checks work the exact same as martingale webbing collars. They are for dogs that slip their collars with ease. They are meant to be loose fitting but when tightened fully they tighten just enough to keep the collar from slipping over the dog's head. These are NOT meant for training, they do not have the same effect as a chain martingale collar or a choke chain.
Choke chains are long pieces of chain that don't have a limit to how far they tighten. They are used for snapping corrections. They are NOT for extreme pullers as the dog will hang themselves, they can cause damage if not used properly. They are fitted high on the neck, directly under the ears and chin, not low on the neck. They are for dogs who are walking beside you in a direct heeling position. Fur savers are choke chains with larger links that prevents fur loss.
Prong collars are for dogs that need a sharp correction that will snap them out of a drive / attack. They are again used for dogs that are in the direct heeling position. They do NOT tighten fully, they have a martingale chain that keeps them from causing damage when used properly. I do not recommend this collar unless you have an expert instructing you on how to use it. They do not stab the dog, they fold in and slightly pinch. These collars are very expensive and should only be used for extreme cases. NEVER use large prongs, they are ineffective and fold huge chunks of skin at a time, always use small / medium prongs. (this advice is from Schutzhund competitors and trainers that I know, they are used on working dogs).
Dominant dog collars are thin pieces of rope that have a bolt snap attached to them. They are placed in the same position as the choke chain (very high on the neck, beneath the chin and behind the ears), the bolt snap is placed on the trachea. When a dog is poised to attack the collar is tightened like a choke chain until the dog releases or stops the attack. These collars are extreme, I will never use them on my dog and don't suggest EVER using one unless you are a trainer.
Harnesses
Front lead harnesses are ones that do not have a martingale attachment in the front, but do have a ring. They are excellent and are much easier on the dog's shoulders than a tightening harness like an easywalk. They fit like a triangle, high on the chest and around the barrel, the should never sag on the chest, as this will damage your dog's shoulders.
Easy walk harnesses are front leads with a martingale loop on the front that works by constricting the shoulders, asking the dog to slow down. Recommended by many for extreme pullers, but people are slowly realizing how much damage it is causing for dogs. Not recommended personally...stick with the front lead. These images are of a PROPERLY FITTED harness! This is what they are supposed to fit like, you shouldn't have to clip the front ring to your dog's collar or it is too loose.
Hback or roman harnesses are what you see at most pet stores, they are good for every day walking on dogs who have sensitive necks however they should never be used for pulling as the front ring digs directly into the breastbone causing long term effects. They are great for dogs who don't pull though! I also like the kong brand one's padded handle, nice for city walking.
Step in harnesses are fitted around the front legs and girth, with no neck piece riding where the collar would. Excellent for walking and much better than the Hback for a dog that could pull. Great for dogs with sensitive necks.
Mesh vest and regular vest harnesses are good for seatbelts as well as for tracking ect. They have a huge chest panel that keeps weight off small areas and spreads it. Not to be used for racing or bikejoring as they are not padded properly (personally I love these things, I use them for hiking too because they act as a chest protector).
Utility Harnesses are like saddles that have a handle on the back and fit like a triangle. Wonderful for hiking since you can tie the leash onto the harness, you can also attach saddlebags, flashlights, and side patches. I personally have a chestplate on mine since I use it in the car.
Webmaster harnesses are amazing. They are inescapable, have a padded chest ring and belly pieces, have a huge but flat handle that won't get caught on branches...I can't give it enough praise. BUT don't use it on dogs that pull for just walking, you're going to be taken for a ride.
For info on racing harnesses (info that I know, I know there is more info out there) click here --> viewtopic.php?f=18&t=4932
Hopefully this clears up some confusion. I know some trainers that are trained with the new methods (all praise and no correction) may disagree with me, but these are the things I have learned from trainers with 30+ years of experience and working dog as well as pet dog owners. I don't have a picture of my certificate, but I'll try to get one soon. it was a 4 hour crash course on collars and harnesses and I also did the extra two hours for prong collars.
If you'd like info on where to buy any of these products, I'd be happy to help.
) info folder with collars ect in