Of all the skills one needs to hit a target with a handgun, stance is probably the least important, especially in a defensive or combat situation. I practice a variety of stances because the different stances provide different benefits and drawbacks in different situations. I'm a fan of isosceles, personally, but I'll shoot weaver on occasion.
Sight picture and trigger control are far more important than stance. If you have a good sight picture, and you can pull the trigger without moving the gun, the bullet will go where you want it to, regardless of whether you're shooting weaver, isosceles, or one handed hanging upside down from a tree.