What to do when we feel attracted to holy names other than the mahamantra?

From: Latha
Hare Krishna prabhu , before coming to ISKCON I was reciting many slogas. But after understanding the philosophy, now I am able to accept that Lord sri Krishna is supreme personality of godhead and need to worship Him by chanting Hare Krishna mahamantra. but when chanting the mantra so many doubts arise in the mind like Is this holy name only powerful….. why cant we chant just ram or Krishna,, om namo bhagavate vasudevaya, sita ram, etc… I feel I understand that this mahamantra is the only hope for this kali yuga…. but still mind is wandering. how to get the firm faith that hare Krishna mahamantra is everything