I would reccomend you to visit Brother Islands. It is a unique place, not only in the Red Sea, but compared to diving in the rest of the world also. Dedalus can be very good as well, but is more depending on what you encounter since the reef is not as colourful as e.g. the soft coral on Little Brother or the Numidia wreck. St Johns is, as Ben point out, not very well charted. From what I have seen of the area so far, it is not on par with Brothers, Deadalus or Elphinstone (my favourites in Egypt). Rocky Island can be good for sharks, but in the later years there seems to be less sharks for some reason. So St Johns-area and south towards the Sudanese border is more of a chance. You might find a brilliant untouched spot, you might find zilch.
good luck
Christian