A superset is when you do one set of an exercise and then do another set of a different exercise with no rest. They're normally done using opposite or unrelated muscle groups like biceps curls and skull crushers, or bench press and ab work.
A combination exercise is when you take two separate exercises and try to combine them, like a lunge with a biceps curl or a front squat with a military press (a thruster).
The Problem With Combos
The big problem with combination exercises is that, invariably, the weight used on one part of the lift is too light. For example, in the front squat combined with the military press, you should be able to front squat a lot more than you can military press, so by default you're undertraining the front squat.
A Better Way
A more effective way is to do a set of front squats followed immediately by a set of military presses, using the appropriate weight for each. Sure, there's a bit more coordination required to combine a front squat with a military press, but people forget that there's also more coordination required to front squat an extra 50 pounds.
This is a superior way of training because not only will you rapidly get better at the two separate exercises since you're using the appropriate weight for each, but you'll get better at combining the exercises if you ever choose to do that.
If you can lunge and curl some nice numbers, with five minutes of practice you'll be able to do a lunge combined with a curl with a good chunk of iron. But, the person who just practices that combination exercise will be lacking in one of those exercises.
Other than the clean and jerk, I can't think of two exercises that when combined would be more effective than when supersetted. In addition, the benefits of increased heart rate and elevated metabolism will be even greater with the superset method than the combination method, but the total time spent lifting should be pretty similar.
Put it to the test in the gym and see what you think.