Lightest Construction Method?
 

I'm aware this is quite a general question, but what is the construction method with the highest strength for a given weight (highest strength-to-weight ratio)? I'm planning on making a massive glider (maybe 4m) for a project where weight is the main concern.

Some possible options I've come across in my research:
- Rib/spar method (cf or balsa ribs, probably cf)
- Geodetic ribs (seems like it may add strength over straight ribs)
- Vacuum-bagged foam core (probably Rohacell, but even this seems too heavy, as I need the plane to be very light)
- Composite sandwich (such as what Vladimir's Model and other high-end composite manufacturers do, I will probably use Rohacell sandwich core and Carboline skin)

Please keep in mind that weight is really the most important factor here, and I'm not expecting the plane to survive a large crash but I would like it to survive turbulence and rough landings. Any indication as to which of these methods (or something else) has the highest strength-to-weight ratio is greatly appreciated. Thanks!