The most effective one is the one that works best for you. Whichever tool best fits your scoring style, feels right in your hand, works best with the weight of paper you use, etc. All of the suggested tools are cheap or free, so try a few, then stick with whatever works best for you. One last thing - I want to emphasize what Ron Caudillo advised about scoring - accuracy counts! It's hard to fold accurately without scoring, but with scoring you can fold very precisely. However, your folds will only be as precise as your scores, so scoring has a major impact on fit and appearance. Take the time to do it well, it will really pay off. Enjoy your submarine build!