There is a lot of drama between machines and free weights. Some people live by machines while other people let them rust in the corner of the gym. Before I say what side I am on, I want to explain the benefits of both.
Definition: A exercise machine used for weight training that uses gravity as the primary source of resistance and a combination of simple cable/pulley systems to convey that resistance to the person using the machine
Machines move in two dimensions and are restricted to certain motions. Machines do a great job of isolating muscle groups by taking away the stabilization aspect of an exercise. For example, when you do a chest press on a machine, your shoulders don’t need to stabilize the weight in order to push it. This helps you isolate the chest better and fully exhaust them before any other muscle gives out first. Also machines do a great job of adding volume and help muscles grow a little bigger than free weights.
Define: a weight used in weight lifting that is not attached to an apparatus. For example: Barbells, Dumbbells, and KettleBells
Free Weights can move in three-dimensional spaces. They are not restricted to a certain range of motion. This is very beneficial because it allows the body to train the nervous system. Many trainers call this functional training, because it allows the body to help improve “real-world” biomechanics. Free weights are also used in multi-joint exercises. This is beneficial because multi-joint exercises strengthen more muscle groups at a time.
Now the question comes down to what you want to improve upon!
I believe both are beneficial, but free weights should take up the majority of your workout. In my opinion, having a great physique, without a focus on movement or function is a waste. Improving movement patterns can help you feel better and lower your risk of injury. If you want to improve movement patterns and increase functional strength, free weights will be better. If you are an athlete, free weights will increase strength that better translates to the field. If you want to focus on increasing muscle mass and lagging muscle groups, machines will be your best bet. So I will end this article with a big tip that I've learned from programming workouts. If you want to incorporate both free weights and machines into your workout, I would recommend you do free weights in the beginning of your workout and end with more machine work.