Truthfully, I think most of them are overrated. I think of many modern day designers the way I think of modern day celebrities.
The best are the old school or "classic" designers/celebrities. For example, Chanel and Elizabeth Taylor are classics. Very few (if any) can touch them.
I believe the best designers are still the oldest labels, the same way the most beautiful Hollywood starlets are the old school/silver screen actresses (i.e. Elizabeth Taylor, Audrey Hepburn, Sophia Loren, Vivien Leigh, Dorothy Dandridge, Lena Horne, Marilyn Monroe, Grace Kelly, etc.)
Likewise, very few, if any of the modern designers can touch the likes of Chanel, Dior, or Salvatore Ferragamo in my opinion.
Also, I am sick and tired of seeing every celebrity create a fashion line because it's "in style" (PUN INTENDED)!
Think of something original.
However, I do like Ralph Lauren, Vera Wang, Valentino, and yes, even Marc Jacobs among others. It's just that the oldest are still the "best" (or among the best) in my opinion!