What's the pro cons of free weights vs weight machines?

Been hearing lots from various people - some professional trainer at the gym, some fitness freak, some not so fitness freak.

Considering I have no one to spot me at the gym (I go alone T_T), and I do weight machines (impression is it's safer to me, and the gym trainer commented it's perfectly fine to just do weight machines) - i still do hear from lots of people weight machines are rubbish

Lets hear some opinion