Everything I've read it is:
1. Screw caps
2. Synthetic corks
3. natural cork from trees
in that order of better. #1 is best.
Natural cork can let in a little oxygen, but mostly it's the cork rot
Do the synthetic corks that are now being used by many wine manufacturers
seal bottles better the same or worse than real corks. I would think there
is less of an oxygen ingress.