What is the best setting for this on an iPhone 4? I read somewhere that the auto kills the battery quicker, but the person never responded to if it should be on or off.
1) Best for battery life probably is off and have it very low.
2) Best for looking at the gorgeous screen is to have it off and somewhere close to 50% brightness.
3) Best compromise might be setting it to 50% or just under and turn auto brightness on.
I go with #2 because the iPhone 4 battery life is very good and I love to see see the high quality screen in all its colorful goodness. Since it's hard to give an exact percentage of brightness I'll say that mine is set between the two letters in Auto-Brightness.
If I'm wrong then it's ok with me because I'm happy with how things are going so far.
What is the best setting for this on an iPhone 4? I read somewhere that the auto kills the battery quicker, but the person never responded to if it should be on or off.
IMHO the light sensor uses an insignificant amount of power compared to the display backlight. Try 'auto' with a comfortable slider setting, and see if it works for you in your environment and usage...