Setting posts

[whistlepig]

I'm getting ready to put up some fence for horses, should I use the 12 inch auger or he six inch auger. My initial thoughts were to use the six because it seemed like it would be stronger. After reading these replies I'm thinking it may be better to use the 12. What do you guys think?

I have two augers. A 9" for 4" line posts and a 12" for 7" corner posts. A good combination for me.