When your puppy is too young for the groomer but wears a stylish collar be very careful of her little neck that is growing every day. It seems obvious but you would be amazed at how easy it is to overlook the pretty collar's size. It seems to be shrinking as puppy grows. One day poor puppy wakes up to find that he is in a very tight, miserable collar.
Every few days put a couple of fingers in between the puppy collar and the little neck. Fingers should slide in easily.
A loose collar is a health hazard as well. I can remember a puppy howling in circles because his little bottom jaw got caught in his collar. Poor little fellow. The collar should be just able to accommodate your two fingers but no bigger.
A big collar seems comfortable but puppy could become frightened by something and back out of the collar faster than the speed of light.
I like to see my puppies in harnesses when they are on leash. The harness is safe and if it fits nicely they can't escape when they are frightened by something like a passing truck.
Dress your puppy well. I like my collars sporty, some like diamonds. To each her own.