avira is good.avast is also good provided it has constant internet access because in latest v8 avast uses many technologies which are dependent on net access for best protection.because of this avast updates a lot(sometimes 20-30 times in a day) so it may be an issue if you use limited net connection.trend micro is heavy & i wouldn't recommend it when there are lighter & free options available.
In the Avast free version, there are Web shield, mail shield, network shield, p2p shield, IM shield and script shield.
THESE ARE NOT REQUIRED AT ALL IF YOU ARE OFFLINE.
you can easily change update interval and settings. Reputation service and streaming update can also be disabled.
till last year's January, i was able to update the definitions quite easily on 2g. then i got a better connection.