Fixing Current vs Voltage in Transfer - (Oct/24/2008 )

I want to get some input regarding transfering proteins into a membrane. Usually what is better: to fix the current (A) and let the voltage vary or fix the voltage (V) and let the current vary?

I have always used fixed current and the voltage was varying (but only max 25 V). But I can't say, if the other way round is better or worse. Worked good for me this way in semi-dry transfert to PVDF.