Don't get me wrong I like (and still use) AdAware - but it doesn't have the teeth it once had (they keep coming to agreements with companies to avoid lawsuits and removing definitions - MS are doing the same with their AntiSpyware product too).
My biggest issue with Lavasoft is that I don't totally trust them any more to have their users' best interests at the forefront. I know that a firewall that isn't updated often enough and allows new threats through will not stay the course very long, but I bought AdAware some time ago and then went through a period where they didn't supply any updates for months on end, stopped responding to emails, and for a time their site didn't seem to be available. Aft that confidence has taken a big knock for me. Now it is one of about 4 spy detection products I regularly use, but it isn't the top dog for me any more.
The whole saga was documented at the time in Fred Langa's newsletter, and he has stopped recommending Lavasoft these days.