Cardiovascular activity is not going to build muscle the way working out your legs would... And your largest most energy burning muscles are located there! I split up my muscle groups as follows:
Day One: Chest, Shoulders, Triceps.
For chest I do free weight bench press, and incline bench press. Machines are ok to begin with because they ensure that you are performing the motion properly but you will not work your stabilizer muscles at all and these are VERY important in preventing injury and building strength.
For shoulders I do Shoulder press with free weights. For triceps I go to a machine.
30 minutes of cardio.
Day Two: Back and Biceps.
I do machines for these, row and lat pull down. Then I do bicep curls with free weights.
30 minutes of cardio.
Day Three: Legs
I go to the leg press (BIG Muscle group!!!). I also do my hip abductors and inductors on the machine. Sometimes I'll switch it up with lunges but if I do legs I don't do any cardio.
Day Four: Core
I do cardio first on core days, I'm usually on the elliptical or the bike because my legs are killing me (lunges

)
I do sit ups and planks.
Then I start the cycle over taking a day of rest.
Having a plan is a good way to keep on track.
So the best machines to do to get the most bang for your buck:
LEG PRESS
BENCH (but eventually you'll want to use dumbbells to build your stabilizers.)
ROW or LAT PULL DOWN.
Those might be fine to start but after I week I would want to see more focused exercises. You can also push yourself more and are less likely to injure yourself if you are focusing on one area at a time and work on a different group while your muscles are healing. I like to rest after core days because you use your abs for freaking EVERYTHING and they hurt!
You might want to hire a professional and have him/her design a program for you that targets each part of your body and makes it an easy routine to follow.