Depends on how you value your data. I look for consistently high readings at AVtest.org. Of all the free stuff Avast is probably the best. In the August 2106 test, Avast detected:
97.5% of 0-day malware attacks, inclusive of web and e-mail threats (Real-World Testing)
98.9% of widespread and prevalent malware discovered in the last 4 weeks (the AV-TEST reference set)
That still means that:
Four (4) 0-day malware attacks got past the AV Protection
Thirty (30) widespread and prevalent malware got past the AV protection
The ones that consistently lead the pack scoring 100% in almost every test as 1) Kaspersky and 2) Bit Defender. Kaspersky runs about $10 per seat in a 5 pack and the latest offer I gt from BD was $17 for 5 seats.