We are designing a Change password box in our web app. This is part of the "Account page" - not in a dialog.
Where does it feel the most natural to place the "Change Password" button in this case?
Option B seems best.
If you can match the width of the input boxes and save button and make it look decent, that would feel best visually - in terms of uniformity, alignment, eye movement.
If the text boxes end up being too long and it doesn't make sense to match the width of the button, then don't. I'd still suggest option B, i.e. button left aligned to input box - neat alignment and easy eye movement.
These suggestions are assuming:
I don't think that any of the options are very pleasing to the eye. I would take Option B since it's the closest, but I would change your columns widths to all be of equal width.
Doing that would result in the following:
As you can see, it's much more pleasing to the eye. You have equal widths on the columns which centers things horizontally and in doing that you see that the title and button are centered vertically.