Systematic research on haptic stimuli is needed to create suitable haptic feeling for user interface elements. In this study we compared three alternative designs for creating haptic edges for buttons. All the designs compared are based on the physical parameters of graphical user interfaces and thus they are applicable for different kinds of user interfaces. A handheld prototype device with haptic feedback created by piezoelectric actuators integrated in the touch screen was used in the experiment. The designs used were minimalistic (Simple), direct transformation of visual pixels to haptic pixels (GUI transformation) and iterative design (Designed). The amplitude, the number of haptic bursts (haptic pixels) and the delay between the bursts was varied in this experiment. The results showed that the most promising designs were Simple and Designed. Less haptic bursts and less delay between the bursts were preferred by the users. The preferred level of the amplitude varied and thus should be adjustable.