Never install more than one "real-time" antivirus at once (e.g., Bitdefender and Avast together). They will fight over system resources and actually make you less secure.
Kaspersky is widely regarded as having some of the most sophisticated detection technology in the industry.
Excellent at catching "zero-day" (brand new) threats and fileless malware.
Free software has to be paid for somehow. Usually, this means:
You won't get "premium" features like a VPN, parental controls, or identity theft protection.