That is the problem, you never know when they are likely to bite you in the a** and why we don't recommend it.
No way would I recommend uninstalling avast as IMHO it is better, whilst avira has relatively good detections, so to has avast, but avast has for more functionality that you don't get in avira, web shield, network shield, boot-time scanning, to name just those from the top of my head.