You need to define "best"!

Best as in footprint, size, speed, overhead, virus count, etc.

NOD32 has consistently been best for machines that are older with slower CPUs and lower amounts of RAM.

For other folk, Avast, AVG have find free alternatives.

-> But not one will protect the PC against the user. These are still Personal Computers and if you want to install some trojan, then you may do so.