I know, you either go with 0, or you focus a lot on it.
But how much do you need?
I mean, my wizard's 14 ac could as well be 0 withouth any problem at lv 13. But if i plan on having AC, how much of it will i need?
IE: more directly, is there a way to know the BAB of monsters on diverse levels to know if your AC is making any kind of difference?