During our recent trip to Egypt, we found this guide to be extremely helpful. Its information on lodgings, restaurants, and sights is unmatched by other guides. We found it had slightly more information than Lonely Planet Egypt, but we could easily have gotten by with the latter. It *is* nice to have the smaller volume to carry around in Cario, though.
If you get only one guide, make it the Lonely Planet Egypt (unless your plans only include Cairo). If you are spending significant time in Cairo, it's probably worth springing for the smaller volume, too.