If you really want an impressive core and midline physique you need to connect the upper extremity and abs within the same movements. An abdominal exercise that requires you to pull with the upper body, or an upper body movement that demands abdominal stability, are both superior for getting that aesthetic look in the core/oblique/serratus that you want. These movements are way more effective compared to isolated core holds.
This circuit are great examples of movements that combine both! Give them a try as a core “cool down.” Adjust reps as needed and your core will thank you.