Neither - they are for illustrative purposes only.
Personally, I would recommend looking not at the absolute values (ie, the individual numbers) - but instead at the relative values between different search terms.
I meant, for example if you had three search terms in Wordtracker OR Overture, and simply comparing how they rate against one another for frequency. There's no point at all in cross-referencing the absolute Wordtraker and Overture data, as they are from entirely different sources and applications.
so in answer to this question....who should we all MOST believe? I suppose comon sense would dictate you go with the lowest #. that way you can never be upset