I quit drinking and smoking in January and joined the YMCA. I love the come as you are and get down to work atmosphere. I feel great and use the machines primarily. I can only go twice a week right now so I use the machines since I can do cardio at the house. I maximize my workout by alternating exercises and not resting between sets - i.e. go from bench to military press to squats to abs then back to bench, etc. for three sets.
Substitute whichever exercises you like, the important thing is to move from machine to machine to give your muscles a chance to rest between sets while maintaining a high heart rate. I wear a Fitbit and monitor my heart rate and only allow as long as it takes to get set up (less than 1 minute) between exercises. Its like interval training with weight machines. The machines are ideal for this as they have different stations for the same muscle group and changing the weight is quick and easy. I did this once before a couple of years ago and got my best time ever on a 5k. didn't run a single mile beforehand.