Transients are persistent and write to the wp_options. The object cache persists only for the particular page load.  Transients are stored in the WordPress database. The object cache is stored on the server where the WordPress install is located.  Transients are available for the duration of a user session and apply to all page components. The object cache is available only for scripts.  Transients persist only for the particular page load. The object cache is persistent and writes to the wp_options table.