Thanks to my android application twipaper I’m in a great position to judge this particular question.
Since the app already needs to be net-connected in order to download pictures I added flurry tracking to count views for pictures of Edward, Jacob… or Bella.
WOW! Edward wins hands down! 50% vs 30%.
I had hoped to produce an iPhone/Android users comparison but apple put the kibosh on this by refusing to release the iphone version of twipaper (copyright fears).
For those interested in the app search for “twipaper” on the android market.