Free weights mostly for me but I do use machines also. Free weight I feel give you a
more dense muscle base.

I think you need both. you can warm up on machines (pre exsaust) and then go to free weights or you can finish off the muscle with some isolation. you can also do supersets using free weights and the machines. there is some things you just can't do with free weights. but I have to agree with irish, free weights for me too.

About the only time I use the machines are legs(not complete leg workout just certain exercises), the cables(love 'em), and if I've injured myself and have trouble with free weights. Like Gorillafit mentioned "normal range of motion" and "stabilizing muscles". When I was just out of college I went to a job that was pretty much 30 hours plus behind a desk on a computer and 10-15hrs in meetings on a construction site. I got pretty damn weak doing nothing but working a mouse and keyboard. So, I decided I'm gonna start working out. Get to the gym and do nothing but machines, no free weights. My joints started getting sore as the resistance went up and on top of that I really didn't notice any "real world" increase in strength. Couldn't really do anything strength wise i couldn't pre-exercise regimen. The repetitive unnatural range of motion doesn't work for me.

Free weights, due to a more natural range of motion, as opposed to machines that lock you into a particular motion. Normally designed for the "average" person.
Free weights also normally bring in more stabilizing muscles and core into play.
Edit: Machines do have their place especially if you have some type of physical limitation that doesn't allow you to handle the loose weight. And cable machines are great, they provide a lot of versatility!