Depends on what you want to do??
If you want to build mass, there is nothing better than basic free weights - Bench, Squats, and Deadlifts. If you want to gain definifition after you have the size, machines work very well. Also most machines are designed to take pressure off joints, if you have injuries or aches. They will build mass also to some extent, but you don't use all your stabilizing muscles like you do with free weights.