i have to vote for story. sandbox is fun, but a story can drive games to greater heights where a sandbox would fail. and all in all, a sandbox feature would take less time to create and could be added in towards the end of creation. a story cant be added in at the end of a production and still be outstanding. i myself love sandbox games but it would be better in my opinion to play a game that could have sandbox features but doesn't, than to play a game with sandbox features and a story mode that just doesn't play well.