Just goes to show - I use MSE as well and I just ran a scan using Malwarebytes - result? 0 detections....mind you I do use an app in my browser (Chrome) called DoNotTtrackMe which blocks quite a bit..in fact it is registering 3 sites trying to track me while I am writing this on the forum...
 
Point is that all the apps for these purposes can all miss stuff - even the same app! Careful and very cautious "webb'ing" is the only tried and tested way of avoiding these things imo.

Bob Bone - I've been using Avast with I think pretty acceptable results so far. No speed reduction noticeable if it's on or off.

I'm using MSE and MalwareBytes Pro and I'm not having any problems. The MalwareBytes Pro detects incoming stuff once in a while and gives me a little pop up notice. I usually run a scan once in a great while but rarely find much. So the combination of the two seems to work okay for me. Neither one interferes with my other software and I haven't had any virus issues for years now.

brconflict
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. 

I try to avoid the ones where the owner of the company is on the run for murdering his neighbor over a dog's barking.  (seems like their ability to focus may be impacted a wee tiny bit)
 
Bob Bone
 

So does he - #18.

You got me, Alex - I didn't look at the link. :)
 
Bob Bone
 

To be honest, I really hate anti-virus almost as much as having my computer infested! I just use Windows Defender and protect myself from foreign media, suspicious sites etc.  If my computer becomes infested  (just a couple of times in more than 10 years because I wasn't careful enough) I would then be motivated to pay and /or  invest time on disinfecting it.
 
At the end of the day our DAW are not for web surfing after all (even if it is just as a hobby like in my case). 

For my DAW, under windows 8.1, I use the included Defender.  Same for my office computer.  Savvy users are usually fairly safe with this.  Less savvy ones need to be protected from themselves with something a bit more aggressive plus need some amount of training about what not to click.  We prefer ESET NOD for our business customers - especially where central monitoring is needed.  McAfee and Symantec tend to be bloated and over-zealous.
 
We have actually setup virtual machines with Windows XP and Internet Explorer 8 and then literally performed tons of searches and clicked on everything - win free ipods, get help from a cartoon ape ads, etc :).  We weren't able to infect the systems.  Yet, we see people every week with all sorts of "fake AV" type scare-ware infections, FBI viruses, etc.
 
As an aside, backups are super important these days with some of the nasty stuff that's going around, like the much reported Cryptolocker.  If you get this one and don't have a data backup, you're kinda screwed.
 
If you want a good third-party look at the whole lot of most popular packages out there, you can find one here with some great reports.  Based on this, you can see that it's about a separation of about 6% or so between the low end (the out of the box MSE/Defender) and the best option.  Here's the link - it's worth a look: http://chart.av-comparatives.org/chart1.php (this is the "real-world" test result - it's a dynamic report/chart).
 
Hope the helps.

CakeAlexS
But hey, enough about what I think, here is a message from John McAfee:
http://www.youtube.com/watch?v=bKgf5PaBzyg

LOL, this video is a riot... could easily replace him reading the letter from a computer graphics designer to a SONAR user!

Blades
As an aside, backups are super important these days with some of the nasty stuff that's going around, like the much reported Cryptolocker.  If you get this one and don't have a data backup, you're kinda screwed.

+1... also you want backup drives not connected to the machine unless backing things up... that one supposedly will encrypt any connected device it can get to.