Hi Cornel,
The Google Webmaster tool indeed looks more accurate - but it doesn't give me an average search volume on Google, moreover it only provides with the impressions of our website for relevant key searches.
Furthermore, the Avg position on there doesn't seem accurate, as it displays 2.5 for one of our keyphrases, even though we've consistently been ranking #1 for the past 6 weeks.
What I don't understand is why the Google adwords tool would give an average search volume of 15,000 in the US for keyword X when the webmaster tool gives me an impression rate of 360 for the same keyword. The two should correlate, shouldn't they?