I have never used Windows 8 which has its own inbuilt anti virus programme, which is similar to Microsoft Security Essentials and is known as Windows Defender.
However, should you install something else, it is claimed that Defender will 'back-off ' and will Not conflict with an alternative Anti Virus programme.
Avast and AVG are highly praised. It's worth having a browse of the following.
AVG is better suited to older computers....Avast is highly recommended.
MSE is now regarded as poor...even by Microsoft.
Way back in July 2014, Computeractive magazine recommended that you
should stop using MSE because it was "worse than useless" and use Avast instead.
I have no personal experience of Windows 8 (I am awaiting Windows 10 before taking the plunge!)
I'm using AVG free on my current desktop and a laptop both on Windows 7. I have experimented with the other main free contenders ie. Avast, Comodo, Kaspersky and MSE.
In my opinion I'd go for either Avast or AVG.
I also have the free version of Malwarebytes, which I 'run' every week.