Auto brightness all the way. I used to keep a brightness toggle widget on my home screen, but I found myself forgetting to toggle it most of the time and left it at 60% for most of the time, but it would be too bright in the dark, and too dark in the light.
I would toggle when I needed to, and then forget about it later when I entered a different situation (go from light to dark and the thing is blinding, or dark to light and I couldn't see anything, let alone where the toggle Icon was!).
So now I just use auto. The convenience, combined with the freed up homescreen real-estate, is a much better tradeoff IMO. My phone only drains at about 2% per hour with mild-med use, so I'm not really caring about the additional drain.