Dress for the Wedding

I'm going to wedding of my friends in June. And i have a huge problem!
I need some nice dress, but I have not Idea what kind of dress I want wear?
May be one off them:

Stella McCartney

Donna Karan 

 Stella McCartney

 Vera Wang

Stella McCartney

 Gucci

 Donna Karan

 Tibi

 Marc Jacobs

 Nanette Lepore

 Herve Leger

 Parker

Tibi