Plywood, for the uninitiated, is built by alternating the grain direction on each subsequent layer (ply). As has been pointed out, wood movement is lowest along the grain, higher across the grain. The alternating plies provide stability.
Equal thickness, quality hardwood plies without voids produce a superior product. Compare a nice sheet of 3/4" Baltic Birch to common 3/4" material you'll find at the local big box store. You'll find a variety of constructions, many with a number of thicker softwood plies or even mdf as filler. You'll also probably see a number of small voids. It keeps the price down and is perfectly suitable for many applications. I don't believe that it proves less stiff to any real degree. Stiffness is largely determined by the thickness and integrity of the outer skins. Think I-beams, engineered joist or composite foam core construction.
If an exposed edge is required on your project, edge banding can be used. No amount of filling and sanding makes a presentable edge with these panels imo.
Marine grade plywood comes in a variety of face veneers, is void free and uses waterproof/heat resistant glue (Ive been told that practically all ply uses WP glue these days). Meranti, aka Phillipine mahogany isnt a true mahogany but is likely the most common surface veneer in marine rated panels. Other options are available but can be ridiculously priced.
Grades AA, AB, AC refer to the quality of the face veneers but say nothing about the panel make up.
Some cheap Baltic birch panels mat have a number of voids. The BB at home depot is not the same product thar I buy at Edensaw. I do use it from time to time though.
I've always wanted to try Richlite panels but they're beyond my budget.