I'll try to help give some easy distiction between many fragrances you come across.
Designer - Donna Karen, Ralph Lauren, Hugo Boss, etc. These are all companies that are mostly cloth designers but dabble in scent creations. They happen to be huge, muti million/billion(maybe) dollar companies so they turn into creating everything a person needs to go out (shoes, colognes, and of course clothes). That is how I usually think about it. I've also memorized many of the designers and houses so it has gotten a lot easier to tell the difference.
Niche - A lot harder to describe. Usually, they are fragrance houses that cater specifically to the creation of perfumes/colognes. Many also make candles but that has to do with scent so it's related. An example is L'Artisan. That is a niche fragrance house that creates a fine line of more exclusive fragrances. Some common characterisitcs of niche fragrances are: harder to find (not in dept. stores usually (creed is an exeption)), more expensive, less generic, higher amount of natural ingredients (in some cases).
The line that separates the two types is a little fuzzy. I hope this helps a little...