Don't become a one trick pony, try a lot of tools, and use a lot of them... If you're stuck with one, you might find yourself in a dark whole at some point, because your tool missed some very important stuff.
someone posted this URL few days ago. the domain popularity tool is pretty handy http://www.linkvendor.com/seo-tools/domain-popularity.html
here is some tools: www dot seochat dot com/ www dot webuildpages dot com/tools/ nice and easy to use tools.... just check it out...
Hitwise is wonderful, though outrageously expensive. For SEO purposes, you can't beat SEO Elite (or similar tool---there are many, many alternatives) and a deep content analysis of the competition. By understanding the competition's link strategy in conjunction with their content strategy, you can typically reverse engineer their SEO campaign.