AVG 2013 Free (make sure to get the correct bit version for your computer) is a great antivirus & system tuner in one. TM uses it himself. So do I, but not on all of my Windows installs. The system tuner alone will purge over 1GB of junk from a virgin install, one that's been used for months, possibly a lot more.
A lot of which is no longer needed Windows Update temp files, just dead weight consuming drive space. AVG 2013 Free also has more features than one may think. If one pays attention to the install process (many blindly clicks through everything), it'll be seen that there's a lot of protection options pre-configured for the install. This includes "realtime" identity/mail & web protection & the AVG Link Scanner.
TM does use other tools to compliment AVG & I'm sure that he'll add further input. I just want to vouch for how good AVG does, w/o heavily impacting system performance.
On the OS's that I run AVG 2013 Free on, I also run MBAM Pro (Lifetime) which can be found at promo pricing for around $10 to $12 & SuperAntiSpyware (free version). All can be obtained from File Hippo. MBAM Free becomes Pro simply by entering a key upon purchase, if desired.
FileHippo.com - Download Free Software
There's also many other excellent software offerings on this site.
I also don't care for MS's spoon-fed security, though for those who doesn't care to install/maintain security, WD is automated. Makes several scans per day. Only thing is, MS's security is steadily shrinking in catching malware samples, as proven by an independent (no ads allowed) testing lab, AV-Comparatives.
If you care to read on:
MS didn't even make the above chart.
Lots of good reading here. MS does make the charts, but never in the yearly overall top five, nor top 10 for that matter.