Bitdefender Free - Offline signatures, cloud detection and good behavior blocker. Updates for about twice a day on my observation. Notifications for detected/cleaned malware sometimes late for up to 1 minute or more (somewhat annoying). Even if protection shield is OFF, still the AVC component works, even if exclusions have been set (super annoying). Generally light on the system, especially after finishing a system scan. However on my old netbook, malware removal causes system slowdown. Setting of exclusion is not good - must be detected/quarantined first before it could be excluded.
Sophos Home Free - average detection, centralized management via web. Good web blocking. Heavy on the system - CPU and HDD reads. Has many processes.
360 TS - My favorite before when I was a beginner in security. Will never look back. Much bloat, signature updates delays.
Kaspersky Free - so good, with heuristics, keyboard, and KSN cloud. Yet it conflicts with my hybrid shutdown/hibernation, so no choice but to uninstall. Maybe on my system only.
My choice: Bitdefender Free - could stand on its own, for a careful user. Just my 2 cents.