If you have the money to invest, Market Samurai is pretty good. Wordtracker is good as well.
But you must remember that keyword research tools are just that - tools. They are a just a tool to help you with keyword research.
I personally have not used any paid keyword research tools in a long time. Everything I use is either from Google or is online(SpyFu, Keyword Spy, etc)
Honestly, I have had much better success with using Google than I have had with any previous keyword tool.