There have been posts on this topic before (including your own), reading them might give you a better grasp on the topic-
http://www.sciencebuddies.org/mentoring ... 3549d5e905
http://www.sciencebuddies.org/mentoring ... 1d4e67edca
For example, if you were to conduct a study on whether people like Sprite or Coke better, the question could be:
Which do you like better-Sprite or Coke?
Which is worse-Sprite or Coke?
You can also take into account the order of the words, if sprite is first, people might naturally be inclined to choose that over coke. Hope this helps, good luck!