I agree with Tom about dropping the arms down. Think about what movements the character will be making and then model him in an average position for those movements. Since most characters have their arms down most of the time modeling with the arms lowered a little results in better looking shoulders during animation (since you aren't deforming to an arms down position, it was modeled that way to begin with.)
Referring to your original post, the obvious medium between arms straight out and straight down is 45 degrees down, halfway between out and down.
Referring to your original post, the obvious medium between arms straight out and straight down is 45 degrees down, halfway between out and down.