as g26 said, it all comes done to the feel you want from your clutch. this is also affected by the type of shoes you choose, and if you mix them up to get even more feels from the clutch. if you find your self tightening the clutch nut in alot then yes go to a heavier spring. but this same feel can also be affected by your diffs and the fluids you use in them. then again also your gearing will affect feel too. along with motor tuning and pipe you choose for your motor.
what car and motor and pipe are you running?