The best keyword research tool that I personally use is Google adwords and I am very must satisfied with its results. Hope this help!
I would stick with the Google keyword tool. as far as i am concerned all other keyword tools are second rate. Most of our customers or prospects search on Google anyways so it just makes sense to do research on that platform, I have found no need to use any other tool.
Google adwords is the one of the best tool you can use, there are a lot of free tutorials you can check online too.