It is really pretty simple, if you have limited time and want maximum results, then favor multi-joint exercises are simply the best. Why?
They work a number of muscle groups at one time, and they have good carry over to activities of daily living and sports. In addition, and maybe more importantly, they are good at maintaining muscular mass, as you get older. There are some muscle groups, like the hamstrings where individual training is more effective. As we age, we loose muscle, and that means lower metabolism and the gain of fat. For that reason, the following exercises or some variation should be part of your weekly routine. Remember, no matter what your goals or what you do, you should perform resistance training exercises at least once, if not twice per week. Cardiovascular activity will simply not work your body to the intensity where you will either add or maintain muscular mass!
Bench Press with Dumbbells. Best done with rotation where as you push the dumbbell up, your thumbs rotate towards each other, as this promotes shoulder function.
Leg Press. Possibly the best leg exercise because it works the glutes, quadriceps and hamstrings without undue stress on the back. Make sure you back is supported, and the kneecap stays aligned over the big toe during the movement.
Lat Pull down. Rather than pulling behind the neck, lean back at a 25-30 degree angle and pull to the chest, where the second button of a golf shirt would be as this engages more of the Lats!