Free doesn't always mean the best.
The better paid solutions will offer more features and overall better security. (Such as Firewalls, Anti-Malware, and more)
Whether that extra security is something you actually need or not, only you can decide. It really depends on how you use your PC, and how often you may put yourself in possible danger.
Some need it, others do not.
If you find yourself getting alot of trojans and viruses, you may want to consider one of the paid suites such as Norton or Kaspersky.
If its rare such things happen, a free solution may be more than enough.
As far as the best free solution though, many here will recommend MSE.
The Firewall built into Windows should be more than enough for most.
Also, a secondary On-Demand scanner is good to have. Malwarebytes is typically the most recommended.
And for the record, Im not saying theres anything wrong with a free solution such as MSE. It works perfectly fine for many.
Simply, some need more protection than it offers is all.