I'd go MSE over Avira. Avira has lower detection rates and their hueristics are fubar. Every single crack or keygen or script is apparently dangerous according to Avira. Plus you have to hack around that awful avnotify.exe that Avira loves to spam. Hate to say it, but Microsoft has the edge this time. MSE is a smaller memory imprint as well.
I don't run AV myself but when I'm fixing machines it's MSE I install. I usually put the setup file the malwarebytes as well, 99% of the time malwarebytes will solve any problems.