We have used both, and Spy Sweeper(the first link) seems better of the 2. Both are free for home use, the professional ones you can buy for not much too, I use the home edition and it is great.
I watch Tech TV a lot & they suggest using both (Ad-aware & Spybot) . . . it seems that what one misses the other one catches . . . I personally use Ad-aware Plus (the paid version) . . . with their new version SE now out, I think will be a great improvement. . . they have changed the way it looks for things . . . it's really heart stopping the first time you use one of these programs & see exactly how much spyware is on your system . . . I started using Ad-aware after having our computer for only a few months. . . in that short amount of time, there were over 200 items found! If you care about your privacy. . . use something - anything . . . Hugs, Magic Lizzy