3) Google: This is pretty straight forward but it’s the main reason I like it. I search for my main seed keyword in Google, and use the keywords that Google itself highlights in bold on the search results, plus the “Searches related to” section at the bottom to get keyword variations or LSI. That’s basically what Google is telling you that topic is about. No need for a thousands other tools. I use these to optimize the on page of my target pages as well.
Finding the best keyword research tool also depends on your own experience with SEO subjects such as buying keywords, long tail content, long tail SEO and using low competition keywords. For instance, a newbie looking to use long tail marketing may find something like Long Tail Pro V3 a little too confusing and a bit expensive as it’s a monthly fee and has a confusing interface.
It would be great if you can provide comparative analysis of this tool with Google Keyword Planner. Since you’re using this tool so you can provide best comparison. One differentiation which I understood is that this tool works for yahoo and bing as well whereas Google keyword planner works only for Google but Google being a dominating search engine, gives the highest returns, so only this reason may not be enough to buy it.