Monty: Some questions to ask/consider:
1) Is it direct entry aircrewman or do you have to join another branch and request/beg for a transfer. If this is the case the branch you join does not have to let you go. Don't let a recruiter who needs more stewards tell you otherwise.
2) Where do you want to live? - RN SW England, Yeovilton or Culdrose. If you consider the RAF then Brize Norton, Odiham or Benson (assuming crewman).
3) Do you want to spend much/any time at sea?
4) RAF crewmen qualify as Sgts. Significantly more cash and status for a similar role as RN crewman.
Sorry I can't tell you the exact eyesight requirements. They will be in AP1269A, or ask your recruiter to contact someone who knows, maybe take them a copy of your previous eyetest for an informal check?