Depending on the size of your dog, his disposition and your training needs there are a wide variety of dog collars to choose from. When choosing a dog collar for your dog keep in mind the size of the breed, if he has any respiratory diseases or problems with his trachea and the amount of fur on his neck. A dog collar should fit high on your pet's neck and not so loose that it can slide down near the top of his shoulders. You should be able to fit two fingers between the dog collar and your dog's neck to achieve a snug fit that won't restrict his breathing and also won't let him slip out of it. Frequently check the size of a puppies' neck to make sure he is not outgrowing his collar too fast.
You can find high quality dog collars made from many materials including leather, suede, nylon and fabric over nylon that all have special characteristics you will want to consider before buying a collar for your dog. For instance, leather collars are a very popular option but if you have a dog breed that enjoys chewing on leather chances are he will tear through the collar fairly quickly. Also, leather isn't a good material for a dog who loves the water so if you have a spaniel or retriever you may want to go with a nylon collar instead since it will hold up much better when wet.
Many pet owners enjoy the look of spiked dog collars but as an owner you need to be careful about how long the spikes are and how long your dog wears such a collar. Bulldogs, Rottweiler's and pit bulls are all popular breeds that can be seen sporting spiked dog collars but mostly these collars are for show and should only be work when walking your dog since you will have an eye on him. If left alone, a spiked or studded collar can actually be dangerous for your pet and other animals around him. Some spiked collars have spikes up to 2" long which can be dangerous to a dog's neck or another dog that is playing with yours. Save the spiked collars for special occasions and don't ever leave your dog alone with one on.
Another choice for a dog collar is a training collar but this is a special type of collar that should only be worn when training a dog. Martingale collars and prong pinch collars are effective tools for training a dog but should only be used by owners who know how to properly size a dog's neck since these collars can be harmful to a pet when not used correctly. If in doubt consult with a dog trainer on which collar makes the most sense for your particular breed of dog.