Sycraft
Microsoft Security Essentials (or Windows Defender in Windows 8, they keep changing the name) has one of the lowest detection rates you'll find, about 90%, because they don't want to have false positives. They do well in that regard, they are pretty much 0 false positive all the time, but it is a tradeoff in detection. Good for regular users though since many non-technical people get pissed at false positives.
 
If you are willing to spend money, I recommend ESET NOD32. It's detection rate is good, and it is quite fast. You can also set it to exclude extensions like WAV, NKI, NKM, etc to it doesn't mess with audio software.
 
For the highest detection rates, look at Kaspersky. Still not 100%, but tends to be the highest out there. Trend Micro also tends to be good but is really slow.

 
Not disputing your post because I have seen tests showing that Kaspersky has the highest detection rates, but I sometimes wonder about the methodology of these tests.  I have had to clean many a friend/relative/neighbor computer who chose kapersky based on reading about how good it is.  Based on wha tthe malware ended up being, it lead me to the conclusion that no program can protect people from themselves.  i think these tests base their results on how saavy anti-virus software engineers would surf the web and not how the average joe does.

Well let me eat my words, ZoneAlarm still uses Kasperspy. So I am still running Kasperspy engine... backpeddle.... OK it's great!!! ;)
 
> but I sometimes wonder about the methodology of these tests.
 
The debate would be 100 times more lengthy than 64 bit precision engine.

I refuse to get in 64 bit precision egine debates because I still don't know wtf that really means

Colin, did you look to see what kinds of threats those 111 hits were? Most likely they were tracking cookies and other mostly innocuous things, and probably not things that were contributing to your slowness. The real culprit's more likely to be some legitimate process, perhaps even antivirus or firewall software, or Windows Automatic Updates. Windows itself is, after all, the most pernicious of viruses.

Nothing can protect users from everything. Virus scanners are just a backup to good security practices, not a panacea that allows users to do what they want. However, some are better with detection rates than others. They are more aggressive in their detection methods, they update more often, etc. MSE is pretty low comparatively, given that they don't update all that aggressively and want to never have false positives. So you can get better protection with a different scanner. Still not 100% though. Nothing is 100%.
 
Security is vigilance and defense in depth, not a single program.

Sycraft
MSE is pretty low comparatively, given that they don't update all that aggressively and want to never have false positives.

Maybe that is why Microsoft offers also Microsoft Safety Scanner, as a complement to MSE ?
 
 

I usually read reviews on the top 5-10 anti-virus/Internet Security solutions and jump ship often. The point being is that each year, they're all competing and some shoot out from the rest as being on top. This year, I'm subscribed to Bit-Defender, which I find quite easy to use, and seems to protect my PC quite well.
 
Sometimes, the ones I avoid are the ones that were acquired, such as Norton (Symantec), Trend-Micro (Cisco), and others that just are dated. Many times, the new-comers are more innovative and seem to avoid time-costing change-management for patches, etc. and hire more inventive and energetic talent so they can more quickly respond to threats and without as much red-tape. Sometimes the under-dog is better. Sometimes the bigger ship simply floats over small seeds that grow into bad problems, and are slow to respond. Sure, the smaller companies are less likely to be responsible, but they do want to take over. They aim to do just that, because they know where the larger ant-virus companies fail. 

Yup antivirus and the weather are related :)
 
But hey, enough about what I think, here is a message from John McAfee:
http://www.youtube.com/watch?v=bKgf5PaBzyg
 
 

If you want to keep yourself covered with more than one antivirus program, why not pick one to do the realtime protection and use the others for periodical scans?

>  why not pick one to do the realtime protection and use the others for periodical scans?
I wouldn't recommend this... See #2. I guess you could get into complicating disabling and re-enabling etc but I don't see the point, and a lot of virus scanner often continue running even though they indicate they are disabled.