One issue I've encountered with Avast a few times on my parents computer is it cutting off the Internet connection when we previously had the paid 'Internet Security' version. The first time it happened, I was baffled over why the Internet wouldn't work, checking Wi-Fi drivers, disconnecting/connecting to Wi-Fi, rebooting and so on.
Then I thought about a past issue when I seen McAfee do this and disabled Avast. The Internet started working. I had to uninstall and reinstall Avast for the Internet to work with Avast running.
Although MSE is a poor choice, personally I use it in combination with Malwarebytes Premium and Sandboxie (which I use for testing unfamiliar software and already caught a scam with it), although I'm sure Malwarebytes is performing the bulk of the protection.