I have 2 questions:

1st- I have a ply subfloor that will be getting a 7/16 solid ontop. What is better glueing or staple/nailing. I don't care about cost I care about a better performng floor.
AND

2. Do I need a moisture barrier "just in case"

If your 7/16" wood flooring is under 3" in width (considered strip flooring) then I prefer stapling because I think it is faster, easier and less expensive. And if the flooring ever needs repairing, it is also easier with a mechanically fastened floor than one that has been glued down. But it is hard to beat the "feel" of a floor that has been glued well. It is solid with no movement and less potential for noise from the flooring. If the flooring is over 3" wide, I would consider gluing or gluing and nailing.