Personally I think a dog should have different collars for different things -- I think that for a walk, it shouldn't be able to slip off. But for wearing around the house, it should be able to slip off. I've heard way too many horror stories about dogs hanging themselves and whatnot.

My catahoula will have a martingale for walks -- they are safe and comfortable and won't slip off -- for around the house, a simple collar that can slide off if the dog is caught on something.