For a number of reasons, I feel the best stance for defensive shooting is the Modern or Modified Isosceles Stance, which is described first. I would recommend that if self defense is your primary purpose, 

adopt as much of this stance as possible.

You do however, want to be comfortable in a variety of positions or stances as you of course don't know what kind of situation you may find yourself in and what physical constraints may be present. Are you standing, sitting, on the ground? Are you injured and only able to use one hand; perhaps behind a wall, etc.? So it is recommended that you practice a variety of stances and techniques with both hands, dominant and non-dominant, so you can feel confident in any situation.

At The Well Armed Woman, I speak of being "Empowered, Smart and Strong". Your stance and the incorporation of good technique is part of accomplishing that mission. When your safety and perhaps your life is on the line, an Empowered, Smart and Strong woman is a fierce force. You will inevitably make some adjustments to the stances discussed here, based on your body type, height, weight, strength, physical condition, etc. Practice is key. Your ability to find your stance under great stress depends on it.

It really is most important to AVOID a few bad habits. Those that place you in a weaker position.