I use 1 inch collars by Bison, the 10-16" size works well for all my dogs. I went with the Bison collars because they are the only quick release buckle collar that has been rugged enough for my basenjis. Bison started out as a climbing company so their materials had to be rugged enough for climbers, that quality has also been present in the collars that I have gotten from them.
For martingales and slip leads, I buy from All Hounds Apparel, http://www.allhoundsaparrel.com. She does several different widths. I like at least 1 inch for my dogs for any walking collar and prefer the widest I can get for coursing slip leads.
