I'm the same as p;3. I run Spybot on a weekly basis, and I normally find that nothing is detected. SuperAntispyware is installed and is run about once a fortnight, and always seems to find things that are "not seen" by Spybot. I keep them both as, I suppose, 2 lines of defense. I do have other stuff installed as p;3 does, but find that between the 2 programs I am free of unwanted software.
Have to agree with the others that have said that there is no such thing as the best for spyware.
A magazine article I read some time ago mentioned that all antispyware programs have their, blind spot I suppose you could call it. Therefore they recommended using 2 different programs so that what one would miss hopefully the other would catch.