Chalk it up to my background as a racer: For me, wide is where it's at. I feel agile when my feet are not pinned to each other. I can move in any direction, extend or compress, and still remain in balance and on the balls of my feet.
A wide stance also encourages me to use my feet independently so that I can quickly vary the amount of pressure I put on either ski. If I get caught inside, my inside leg acts like an outrigger to catch me. My inside ankle is cocked so I can easily adjust to terrain changes. And my inside knee is ahead of my big toe so I can feel the snow. This gives me the confidence to roll to a new edge early.
If you've tried shaped skis, you've probably noticed that they invite you to open your stance. I find that the newer shapes let me extend my body, lean inside, and put lots of pressure on the outside ski at the beginning of the turn. As a result, the ski's edge grabs quickly and feels solid even though I'm tipped way over. To start a new turn, I just release and let both skis float.
The trick to clean, strong turns is balance, rhythm and timing-from an open stance. I only tighten my stance when it's necessary to adapt to terrain, such as in trees or moguls.
Felix McGrath was the top U.S. Ski Team slalom racer in the late Eighties and early Nineties. He is also among the top finishers on both the World Pro Tour and World Technical Championships.