Jagadguru Shree Kripalu Ji Maharaj teaches that Radha Krishna have unlimited Divine names, and they are all equal to each other and eternal. Thus we can repeat any name that we prefer, and we will get the same benefit. But please keep in mind that the power of Their Divine names remains dormant unless we take Their names with love and faith. If we remember that Radha Krishna are fully present in each of Their names, and that Their name is another form of Them, then we will begin to receive the true benefit of the name – the power of the name will be revealed in our heart, and we will begin to experience the bliss of the Divine name. It is most important to picture the form of Radha Krishna as we repeat Their names – that way our mind will be attached to the one Whose name we are taking (this is called roop dhyan).