Both Knox and Sollecito should head for a country with no extradition treaty to Italy.
Solecitto has already had to surrender his passport, so he isn't heading anywhere.
As far as Amanda, if she wants to go on the run, her options are limited: in addition to the United States, countries with extradition treaties with Italy include Argentina, Australia, Austria, The Bahamas, Belgium, Bolivia, Brazil, Canada, Costa Rica, Croatia, Cuba, Cyprus, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Ireland, Kenya, Latvia, Lithuania, Lesotho, Luxembourg, Malta, the Netherlands, New Zealand, Paraguay, Peru, Poland, Portugal, The Vatican, Romania, Singapore, Slovakia, Slovenia, Spain, Sweden, Sri Lanka, the United Kingdom and Uruguay.
That basically leaves the Middle East, the African subcontinent and most of Asia. Something tells me she isn't going to be interested in going to places like Iraq, Syria or Iran. Nor is Angola or Botswana going to be her cup of tea. The problem with most evolved regions or Asia (a continent I travel to frequently and know well) is countries there definitely frown on hosting fugitive expatriates. Hong Kong couldn't get rid of Edward Snowden fast enough.