Not one, the kettlebell or dumbbell, is necessarily more superior than the other. They each have their own value to offer.
Dumbbells are used mostly when the goal is to increase muscle size and strength. The weight is even on both ends making it easier to control and perform more fluid movements. They provide a better center of gravity. Movements can also be performed unilaterally for better range of motion. Dumbbells enable multiple muscle groups to be used. Did you know you can even strengthen your core with the use of dumbbells?
Kettlebells are most often used when the goal is power training or when both hands are needed to grip the weight. The weight is directly under the handle and the overall design is easier for power movements and grip. They can be moved around dynamically and explosively. These types of movements help weight loss and improve cardio.
Kettlebells been proven to increase the strength of the trunk extensor muscles. These muscles work in tandem with truck flexors to support posture. Studies have shown decreased pain in the neck, shoulders, and lower back. are most often used when the goal is power training or when both hands are needed to grip the weight. They also increase the strength of the hammies and glutes when used correctly.
When it comes down to it, I choose each according to what my goal is at the gym or at home each workout sesh!
Which is your go to??