For years I’ve been looking for a good screw extractor. So far I’ve had the most success with these: Grabit Screw Removers. While working with several stripped screws (mostly small aluminum and light steel), it removed all but one when used as per directions. I don’t think I’d try removing a screw that has the entire head broken off using these, but they work well for stripped screws.
For comparison, I’ve used Black & Decker and Irwin screw extractors before, but they required much deeper holes to be drilled in the screw, and I rarely if ever managed to remove a screw using them.