Sample, sample, sample!
Keep trying out scents at department stores, Sephora, etc. Don't buy something right away. Take your time, spray it on, walk away for an hour and THEN make your decision.
Acqua di Gio is a fine scent, I would classify it as an aquatic/fresh scent - so perhaps you might want to get a non-aquatic/fresh scent as your 2nd scent, so you have something different. It's up to you.
Grapefruit by Jo Malone is a great citrus scent, but it won't have the strength and/or longevity that the Armani will. What Yves St. Laurent cologne were you looking at (there are so many)?
Have you tried Terre de Hermes by Hermes or Infusion d'Homme by Prada or Rive Gauche Pour Homme by Yves St. Laurent? If not, try these.
Good luck OldSchoolCharm. Welcome to Basenotes!