i want to buy a keyword tool for adsense and adwords which is best?

I want to buy a keyword tool for adsense and adwords. Please tell me which is cheaper and better.Thank you

You'd be crazy to buy..there are so many excellent free ones.

This one: https://adwords.google.com/select/KeywordToolExternal is all you really need. Enter any keyword or phrase, select whether or not you want synonyms and search. This tool tells you the competitiveness of the keyword phrase (in terms of how many other people are bidding on it), approximate search volume for the month of March, and approximate search volume over a 12 month period. You can also (through a dropdown menu) either see the broad volume or exact volume. So if you're searching for health conditions, the broad will tell you any variation of those words i.e. cancer health conditions, but the exact tells you the volume based on just that phrase.

This is the best one in my opinion. I discovered it through http://www.trafficvault.com which has a lot of cool tools (most, if not all were free). From what I've seen, if you want a Google-based tool chances are Google already has made one for free that beats anything else you can buy.

Hope this helps.