No single piece of weight training equipment is best for everyone. Both free weights and machine weights — as well as other types of resistance — can help you increase your strength. The choice really comes down to your personal preference and your access to equipment.
Free weights are versatile and inexpensive. They also simulate real-life lifting situations and promote whole-body stabilization.
Machine weights also can be effective weight training tools — as long as you use machines that adjust to your body dimensions and allow full range of motion of your joints.
The bottom line? Choose a weight training system that you enjoy and that fits into your lifestyle. And whatever type of resistance you choose, remember that proper technique is more important than the specific type of equipment.