I buy collars either for function, or just because I like they way they look. Usually the latter - I get bored easily with just one collar, so when I see one I like and have some extra money, I buy another. Not sure how often. This year I think I've bought one new collar, maybe two.

All of my dogs wear martingales out in public, for training, etc. Keira's been alternating b/w a martingale and a prong lately for re-learning how to loose-leash walk (she's going through a phase in which she couldn't care less about any previous training or what we have to say to her). The prong's only been used these last two weeks though, and already I barely have to use it and we're about 95% back to just using her martingale.

Around the house they all have regular collars for ID purposes. Rolled leather for Winston and Spring, flat leather for Dance at the moment, and flat nylon for Ki.