Let me give a suggestion and a question:
You make use of applications outside the official store Play Store? Or just makes downloading apps from the Google store and arrives permissions ..?
If you make use of external, unknown applications, does not have much common sense and really need an antivirus I would use: Avast Free Mobile
Now if you are a User with a good sense, does only download applications from the google store, disabling the unknown sources, but read the permissions, I would tell you that there is no need for an antivirus, android is based on linux, you needs a very large permission for these 'malware' to take effect (access root or unlocked bootloader). Antivirus for android will just 'do a scan' comparing whether it is safe or not, there is no other way to detect malware. Another thing: the own google the green robot system has a choice: verify applications (ban or warn you before the installation of applications that can cause damage), pure placebo
It is my suggestion, sorry some grammatical error in my English