An Anti-Virus that includes detections for spyware would probably be quicker and more effective, since it can scan for a range of malware all at the same time. Online scanners like the Windows Live OneCare Safety Scanner and s few others can do this and perform other duties like cleaning temporary files, etc.
The other benefit of this is that you are using a different [free] scanner, so you have a chance of detecting something that Spybot S&D or your installed AntiVirus might not.
Spybot S&D is an excellent Spyware scanner when looking for installed malware, since it effectively searches for the links in the registry and other locations that lead to the malware. Howevr, it isn't really effective as a file scanner, since that's what AntiVirus is for.
Bitman