Well, this seems like the thread for me

I tested almost every popular celebrity brand existing (meaning real celebrities, not those wannabes

- if I remember correctly one or two wannabes

).
There are good and bad ones in each.
Of course I love me some Mariah

Forever is my all-time favorite. Followed by M, That Chick, Ribbon and Honey. Those are really nice. Vision of Love was too, but I can't wear it that often.
Jessica Simpson's line (minus the Dessert Treats edible stuff) had good ones too. I have nothing bad to say about those, but Parlux seems to have terminated the contract. Personally I can't wear Fancy, but all others are recommandable.
Both Madonna's are good, although I hate Madonna

Hilary Duff's With Love is wonderful, but discontinued.
Taylor Swift's Taylor as it is close to Fancy Love.
Amanda Lepore is fantastic, but not affordable with $550

Ah, there are too much brands to go through all of them.
I'd stay away from Justin Bieber and Nicki Minaj - those latest additions to Elizabeth Arden are yuck. I don't like Rihanna's stuff at all. Too heavy and stinky or simply blunt. Beyoncé doesn't do it either. Lady Gaga - zero points.
I'm personally disappointed in Kylie Minouge's line - only the men's fragrance Inverse is nice. Shania Twain's weren't good either. Reese Witherspoon's Avon scents too unfortunately.
When it comes to companies Coty has hits and misses. Elizabeth Arden too. Others have few celebrity brands, but there is a nice scent here and there. Back off Proctor & Gamble made scents (Christina A., Naomi Campbell, Cindy Crawford etc.), they smell of laundry detergents.
And I'd stay away from those UK-made celebrity scents, they are by far the worst production wise. If there is a specific line I didn't mention - just ask. Maybe I can say something about it too

You can take a look at my collection and ask about a particular scent if you like.