I've been working with the Google Adwords keyword tool for a while now to do keyword research. Back in the day, I used Wordtracker as well, but I found it to be less accurate. Recently I've thought of revisiting the Wordtracker tool - has anyone used it in the recent past successfully?
The consensus is pretty much that Google have all the data, and hence their tool is the de facto standard for keyword data and research. Wordtracker, unfortunately, have a much smaller smaple size, and so are typically less widely used and relied upon.
There's nothing to stop you trialling and seeing what you think - it may be that their site works better for you. But most people rely on Google these days.