In my spare time I do a lot of malware testing in VirtualBox and have discovered the importance of good anti-virus/internet security software since without it you really are in trouble. Windows Defender has horrible detection rates and will not save you from most threats (had about a 45-50% detection rate for file detection when I last tested it on Windows 10).
The top 5 Internet Security Suites in 2016:
1) Kaspersky
2) Bitdefender
3) Norton
4) Trend Micro
5) F-Secure
I have tested all of these and concluded that overall these are the top 5 in order (1 being the best - 5 being the worst out of the others). Kaspersky, Bitdefender & Norton are all very close in terms of performance, protection & usability and I would say that Bitdefender is perhaps better than Kaspersky other than for the Firewall.
I personally use:
Norton Internet Security 2016 - which is incredibly fast, updates & scans automatically, has an amazing firewall, has saved me plenty of times and is in the top 3 internet security suites.
MalwareBytes - daily scans but only using the free version
Spybot - weekly/sometimes daily scans using free version
AdwCleaner - Weekly scans
Winja - great tool for downloading file since it quickly checks files, process, etc to VirusTotal's database
Process Hacker - a better version of Task Manager
Cleaning tools:
CleanMaster
Ccleaner
Glary Utilities
Wise Registry Cleaner
Advanced System Care
Browser Security:
Norton Internet Security 2016
Avira Browser Safe (The best extension I have ever used - 100% malicious URL blocking on my tests)
AdBlock Plus
AdGuard
LastPass