I tried Microsofts anti-spyware and the thing I like is how much information it gives you about each threat it detected. Much more than AdAware or Spybot. It lets you decide what to remove or what not to.
Ad-aware and spybot ,are unlike microsoft spyware tool ,as they are after the fact removal tools ,and the microsoft one will scan and remove after the fact, but also watches whats coming and going on you computer ,and will block them if they are bad and in the programs database !!! and does give lots of info on the problems .In short I like it .