I'm avast user, both have good things.
Avast: has good .gen detection, stream updates, NG + cloud detection, hardened mode. The downside is the damn ads.
Avira: has good detection, APC is amazing, updates every 2 hours. The downside is that they don't have 0-day protection (scripts can bypass the AV), removal issues and the exclusion list works wierd.
I can't tell you what to use, you should try and see what works best for you.
AVG is a good product too (you can take a look, IDP is very, very good). My top 3 is: Avast, AVG, Avira. I also love Tencent PC Manager (if you wanna use chinese software and you are not paranoid)