The presidential form of democracy should be a better form of government because it would be more of an organized situation than it might be under a parliamentary being due to the fact that the decisions would be going through more of a close knit style as opposed to a larger form.
No one form of democracy is better than others. These forms of governance evolve with the countries that set them up. A presidential democracy works well in America, but it wouldn't work well in England or Australia. Both systems are not perfect, and both systems will have its share of flaws.