First before buying anything do a full trial to see how that software behaves on your system and works for you.
Microsoft Defender coupled with Andy's tools (Configure Defender and Simple Windows Hardening) is a great option.
I find it just a tad too heavy on older systems and prefer F-Secure SAFE (with Simple Windows Hardening on my system) for its lightness and Mikko Hypponen
Bitdefender is a hit or miss depending on your system, so definitely do a trail first.
I just don't like Avast (or AVG) anymore, so no real opinion on them.
Was an Avast user when it still looked like this:
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