The answer is simple, neither.
I personally think that both are essential in any gym workout and provide pros and cons with each goal set.
I myself train with free weights and kettle bells, and train all of my clients with both sets of equipment.
Kettlebells have been proven to be very effective for weight loss, core stability and strength, functional strength, and a cardio advantage due to the swinging nature of the lifts.
Personally i use the kettlebells with clients looking to lose weight and gain core strength.
The hard thing with kettlebells is form and technique for beginners it is something that takes time to learn and needs to be done correctly.
Any beginners wanting to learn the art of kettlebells should definitely sign up to the tips and training strategies to kettlebelling for fitness.
Free weights (dumbbells) are a lot different to kettlebells, they generally isolate muscles more than kettlebells and provide a better pump on that particular muscle.
Given the isolation factor free weights can assist with muscle definition and toning which for a lot of guys in the gym is the main reason they stick to Dumbbells over kettlebells.
Ease of use with free weights is definitely an advantage for beginners.
To finish both are very important in achieving goals and maintaining a fit and healthy lifestyle.
They should both be used to provide variety to someones workout because change is good and we need to work our muscles in many ways.
Train hard, eat healthy and LIVE LIFE...