Oh and the main difference between Sharm and Dahab is that there are lots of Israelis and pot smokers at Dahab, but not Sharm which attracts more package tourists and passionate divers. Just my opinion!!
Dahab's claim to fame as a diving destination is the Blue Hole - about 10 mins north of the resort. Awesome diving and water quality is plenty good. Watch out though - it is very deep and very dangerous!