The lowest ISO I can get away with!
I wrote this article which is on point to your question forWhat is your favorite iso speed and why?
Thing is...there is often not enough light to shoot at base ISO and still have a respectable shutterspeed. For myself, I started having much more success when I shed my fear of higher ISO, and replaced it with a fear of slow shutterspeeds. I'll take 400 ISO anyday if that's what it takes to get above 1/125th. Now, I tend to think of ISO just like film speed, and I start off in 400 iso if its cloudy etc.