There were so many beautiful dresses at this party, but here's the dresses I saw and went "ooooh" for in a good way.
I am going to go ahead and say I think Anne Hathaway's dress was the prettiest with Jennifer Lopez's dress at close second. The dress I would want to wear would be Sienna Miller's, just because I think it's the prettiest dress that's still a little edgy.
**update I just came across Melania Trump's dress designed by Christian Siriano. I am so impressed with Siriano, the dress is gorgeous!
My favorite/best dressed list:
Melania Trump in Christian Siriano

Kate Bosworth in Valentino

Jessica Szohr in Atelier Versace

Blake Lively in Marchesa

Marion Cotillard in Christian Dior

MIA and Zoe Kravitz in Alexander Wang with the designer (they definitely look like the cool kids at the party)

Taylor Swift in Ralph Lauren

Jennifer Lopez in Zuhair Murad

Kirsten Dunst in Rodarte for Gap

Coco Rocha in Zac Posen

Chloe Sevigny in Proenza Schouler
Iman in Prada
Sienna Miller in Emilio Pucci
Anne Hathaway in Valentino
Least Favorites:

Christina Hendricks in L'Wren Scott

Kristen Bell in Diane von Furstenberg

Kristen Stewart in Chanel Haute Couture
Margherita Missoni

Padma Lakshmi in Roberto Cavalli
Tina Fey

Malin Ackerman in Temperley London
Let me know your choices! I'm interested to hear if you agree/disagree with my picks.
(photos from fashionologie.com)