Saint Laurent gown with plunging neckline: Dakota Johnson or Lily Donaldson?

Who wore better this Saint Laurent gown with plunging neckline: Dakota Johnson, in white, at the «Fifty Shades of Grey» UK première held at Odeon Leicester Square on 12th February 2015 in London, England, or Lily Donaldson, in black, at tha amfAR‘s 22nd Cinema Against AIDS Gala, Presented By Bold Films And Harry Winston at Hotel du Cap-Eden-Roc on May 21, 2015 in Cap d’Antibes, France?

Similar dress: Saint Laurent chain-trimmed stretch jersey mini dress available at NET-A-PORTER