There is probably more than one way that will work successfully. Even with a given type of scoring, some teams will succeed enormously, and others will struggle. I'm guessing robots that can "shoot" from a distance, or dump in masses will be prevalent, and if designed well, both have a chance of success. People will have much better insight into "good" methods of scoring once competitions start...
My best advice to you is to pick a design and stick with it- practice with it and tweak it, and that's your best chance at having a successful scoring mechanism.