No single product is 100% foolproof
and can prevent, detect and remove all threats at any given time. The security community is in a constant state of change as new infections appear. Each vendor has its own definition of what constitutes malware and scanning your computer using different criteria will yield different results. The fact that each program has its own definition files means that some malware may be picked up by one that could be missed by another. Thus, a multi-layered defense using several anti-spyware products (including an effective firewall) to supplement your anti-virus combined
with common sense
and safe surfing habits
provides the most complete protection. Always remember that security begins with the user.
I'm not an advocate of suites. All-in-one tools and suites generally use more system resources than separate programs that do the same task. They tend to have varying degrees of strengths and weaknesses for each feature. In contrast, separate tools are designed, built and maintained with a greater focus in a specific area so they are generally of better quality. This means the program's performance for that particular feature is usually superior than their all-in-one counterpart. Further, all-in-one tools generally do not allow the user as much flexibility in tailoring default settings and usage.