I use machines mostly to try to avoid injury. Although my left elbow is hurting right now from the bicep curl machine, so I guess it hasn't helped. I used to have problems with my right shoulder, and that has been good thankfully. I have more problems when I use free weights, or do pushups as I find it harder to keep proper form. So I stick to the machines. I just wish my left elbow would heal.
I haven't worked out in a couple of weeks, I hope to get to the gym tomorrow, I'm trying to get my sleep back on track so I can do it in the morning. I prefer morning workouts for some reason.
I think I'm doing too much weight on my bicep curl machine, so that might be why my elbow is hurting. My workouts are intensive though, and they wear my body out very much. I can't do more than 2 upper body and 2 lower bodies a week. I used to do 3 upper bodies a week, but I no longer have the energy for that. And now my knees have been acting up (I'm on my feet a lot at work too, and do a lot of walking), so I have lowered my lower body to once a week (I also do cardio with lower body strength training as well).
I do 2 types of upper body strength training. One for endurance (20 to 30 reps), and the other day I do high strength (8 to 10 reps). I'm pretty happy with the results from this, but I may modify it more in the future. I like to do endurance because I feel it is a better workout for my body and makes my muscles and body more well rounded (in terms of being able to adapt to different physical duties I may have to do in real life). For endurance I do 3 sets, and for strength I only do 2 (one is more of a warmup with less weight). I read somewhere that doing 3 isn't necessary for high strength muscle building. Plus I can life more weight on the last set if I don't wear my muscles out doing 2 prior tough sets. So my first set is a lower weight warmup to get my muscles adapted to that motion, then I put as much weight as I can lift.