Is a lower armor class always better? For example: does dropping from -4.2 to -4.4 make a difference or do you have to cross an integer boundary (-4.9 to -5.1)?
As a rule, you must cross an integer, however there is another consideration to this. Web affects your AC by +.3, so many will will run with an AC of -7.3, -8.3, etc so their AC doesn't change when webbed.
when u increase ur ac from -10 to -11, it is only increasing half the effectiveness compared to when you increase from -9 to -10. That's a special case..
what is life if full of care, if we have no time to stop and stare?