Weight Lifting Routines: The Difference Between 1 and 2 Arm Exercises
The question of whether to use one arm at a time or both simultaneously for certain exercises is one that I see fairly often.
As the experts explain it, it would depend in part as to exactly what you want to get from the exercise. My reasoning has always been to build the most muscle, you should rotate between workouts, so as to keep your body guessing. Assuming that you can give maximum effort either way, I still think that is the best approach.