Q: Is doing one exercise which works the triceps and biceps more beneficial than working on one machine which isolates the triceps followed by another which isolates the biceps.

A: Honestly I can't think of any exercise, machine or otherwise, that significantly works both triceps and biceps at the same time. Biceps and triceps are responsible for opposite actions (elbow flexion vs. elbow extension). It's more likely that one of two is being worked while the other provides some stabilization. This, for example is the case with dumbbell shoulder presses -- biceps stabilize the arms while triceps get a good workout helping the deltoid muscles push the dumbbells up. But this would not constitute a good bicep workout. So to answer your question, you'll probably want to work both of them separately to make sure they both get a good workout.