Answer
If one is able to chant the śuddha-nāma (the pure holy name), there is actually no difference. One pure utterance of Krishna's name, Rama's name, or Vishnu's name is complete in itself.
However, the scriptural statements about one thousand names of Vishnu equaling one name of Rama, and three names of Rama equaling one name of Krishna refer to the way ordinary conditioned souls chant the holy name in this material world with their tongues. These are transcendental equations given by the scriptures, and we simply accept them because the śāstra declares them.
For a pure devotee, there is no hierarchy or difference. Krishna's name is Krishna, Rama's name is Rama, and Vishnu's name is Vishnu. In the spiritual world, where everything is absolute, there is no comparison or competition between the holy names. There is only transcendental variety.
The scriptures make these statements especially to encourage everyone in this age to take shelter of the Hare Krishna mahā-mantra. Lord Caitanya Mahāprabhu, who is Krishna Himself, appeared to freely distribute Krishna consciousness and Krishna-prema. Therefore, the Hare Krishna mahā-mantra carries a special mercy and accessibility in Kali-yuga.
The scriptures also say that the Lord has invested His holy names with unlimited potency. This does not mean that the Lord and His name are different. Ontologically, the holy name is the Lord Himself. Rather, the "investment of potency" refers to the sound vibration that conditioned souls chant with their material tongues. In Kali-yuga, that audible vibration has been specially empowered to deliver the fallen souls.
The essential truth never changes: the holy name is identical with the Lord. When one chants purely, all of the Lord's full potency is present, because the holy name and the Lord are non-different. There is no difference in potency when the holy name is chanted in purity.
