Actually nothing is perfact, no doubt that Google's keyword suggestion tool is good but sometimes result may vary. In my opinion, I think as asking from the members would it be a good way to go with some good paid tool? What do you think which one is better?
Before starting the keyword analyzing understand your business theme and goal. After that you use free tools like Google ad words. You can get lot of keyword idea from keyword analyzing tools. Short list the best keywords which your costumers like. After finalizing the keyword go and check out the organic competitions and SEM competitions.
And don't forget it is not called a "TOOL" for nothing. It is more important how we use it and less important which one we use. In the end, the good old Google Adwords Tool has made a lot of people a lot of money despite being a bit basic and clumsy to use, SY
As focusing on Google adword, I found date variation many times. And It's obviously kept in mind what we are going to do and what is the theme or focus of the site. As it's just a tool so how could you depend on it. or can we, is it possible?