windows defender is free but i wouldn't say it is a good or feature full antivirus. It only does the basic which is good enough for people who knows how to handle their computer usage.

For users who are not so tech savvy, I would recommend using more powerful antivirus that comes with internet protection.

If you want free then go for free version. If you have a little money to spare then go for antivirus only version. If you have more money to spare and want absolute protection then go for antivirus+internet protection.

Almost all antivirus software comes in this 3 package type: free, antivirus, total protection.

My persona favourite is avast. Cause it is light on memory, fast and have avast manager where you can manage all your PC's antivirus.