I have done both in my '95 Prelude Si. I did all the bushings in Energy Suspension including the trailing arm. You should wait and do both for labor purposes. Not all the ball joints should be bad on your car. Replace the ones that are bad only. You may want to consider the front ties bars as well. But wait, save up and do it all. You will love it. It is like having a new car and the handling is SICK!!!!
Duron