Enjoy the fact they are free and try them all. See what works better for you. In terms of protection they are quite similar. Avast/AVG has been improving although it does have frequent false positive on innocent pages, Bitdefender has its quirks as well. All security software do.
Check for impact on day to day work, see if they don''t interrupt access to wireless devices, if none of the pages you eventually need to access for work load with no problems, etc.
Use the vendor uninstaller r make a system image clean then restore if you decide you didn't like a product.