Which is better AVG or Avast?
Avast paid is better than AVG free. AVG 2015 vs Avast? Preference, but AVG is extremely efficient, and that's why I love it.
I am using AVG Internet Security 2015. The interface is fantastic, and it doesn't have any notable effect on my battery life. I've been getting 8.5 hours at 40% brightness.
If you have it perform a full scan, it will eat your battery, but the background processes like the watchdog service and various automatic scans have no impact on my battery life and never really consume any resources.
Antivirus is a preference thing. Last I checked, I think Bitdefender or Kaspersky had the best detection rates - slightly. I haven't seen any AVG 2015 tests yet though.