I was doing some research on some keywords, trying to figure out whether to buy a domain name and develop a site. As part of my research, I used Google Adwords' Keyword tool. From that, I found a few nice possibilities. I then went to keywordspy.com and checked those same keywords, just to get confirmation. Well, the numbers didn't add up. They both seemed to omit phrases the other would say has traffic. I'm just trying to figure out how much traffic Google is getting for a term. Does anyone have experience with these tools to explain the difference?
From my experience, nothing is actually accurate, but if you are looking for the more accurate I would go with what Google operates itself. When I had conflicts with Market Samurai and Google Adwords tool I went with adwords tool and it appeared to 'logically' be more accurate. There is nothing for sure, though and I doubt anyone can give you a direct "X is more accurate than Y". Good luck, hope this helps.
I agree with others that AdWords KW tool is probably a bit better than most others, and I also agree that traffic estimates are a bit high. However, it is a good guideline. /*tom*/