The best replacement for windows defender is mcafee.

The best alternatives to windows defender are rated as following:
★★★★★  mcafee
★★★★★  norton
★★★★★  avg
★★★★  avast
★★★★  security essentials
★★★  microsoft security essentials
★★  spybot
★★  avira
★★  malwarebytes
★  kaspersky
★  norton 360
★  norton internet security
★  avg free
★  ad aware
★  mse
★  trend micro
★  webroot
★  antivirus
  norton antivirus
  windows security essentials
  adaware
  microsoft essentials
  mcafee better
  spy sweeper
  mcafee security center
  windows firewall
  ms security essentials
  microsoft antispyware
  spyware terminator
  windows essentials
  zonealarm
  spyware doctor
  norton security
  avast 2014
  zone alarm
  trend micro titanium
  anti spyware
  spyware blaster
  spy bot

Your alternative for windows defender is not listed? Suggest!
Speaking about windows defender, one probably shouldn't forget about norton.

Other search terms related to windows defender and their ratings are:
★★★★★ norton
★★★★ avg
★★★ wga
★★★ avast
★★★ mcafee
★★★ security essentials
★★ kaspersky
★★ microsoft security essentials
★★ malwarebytes
★ avg free
★ eset
★ mse
★ avira
microsoft essentials
You have in mind a companion for windows defender and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of windows defender in all years. Click on graph for more.
windows defender
mcafee
norton