To view, edit and save in postgis geometries using OpenLayers + Geoserver what is recomenadado use GeoJSON or serivços WFS? I ask this for performance and additionally want the edition is recorded in the database realtime.
Even if you read the features as GeoJSON, I think you probably need to use WFS-T to modify features.
WFS-T allows you to add, delete and update WFS features. GeoServer supports WFS-T.