Gyms and Workout Facilities: What is the best exercise to strengthen core?The secret behind an amazing core is (1) compound mid-section-centered weightlifting movements to develop raw core strength and (2) dynamic movements/ static holds to develop strength endurance.
The best exercises for core strength are the squat and the deadlift. When you squat and deadlift, you are putting an immense amount of pressure on the body, especially your lower back and midsection (aka your core). Furthermore, you are developing hip driving power and, in the case of squats, the quads/hams/glutes (remember, the lower body plays a large role in core development as well). You will be forced to adapt to this pressure as you lift heavier. These compound lifts are the best moves to develop core strength.
Along with strength, you should have a focus on strength endurance, which involves a mix of dynamic movements and static holds. The best dynamic movements/static holds to strengthen core can be found in many sports. Sprinting is a great example since body-weight must be maintained in a forward direction while you run at a high speed, working the entire midsection. Another example is martial arts, where your body's center must be kept in balance; around that center you pivot to unleash a roundhouse kick while maintaining that balance and return to starting position, keeping your midsection tight the entire time. Swimming is another great exercise to develop strength endurance in the core, as you tighten your body and maintain strict form while on the surface of the water. Lesser secondary movements such as situps/ crunches/ bicycles/ and leg raises also help to condition the midsection and form a balanced core, especially with lesser developing areas (the lower abs, obliques, etc). However, these secondary movements, which you might see people performing maniacally in the gym, really aren't that necessary.
Despite all of the exercises listed above, there is nothing more important than a strong, solid foundation. This can be easy to achieve with some weight training and a healthy diet. Bottom line: squat, deadlift, sprint/swim, and once you feel like you are experienced enough to hit certain areas of the midsection for aesthetic purposes you can do occasional crunches and leg raises (although they are entirely optional for a strong core).