I'm thinking about that. I have both genders of Nidoran in Soul Silver as I type, both sitting at Lv.12. I can't import then yet, and have been hedging on developing them because females apparently lose their ovulational abilities once they fully evolve (whereas Nidoking can breed). Someday I will have to evolve them in there, however.
I guess importing Nidoran into Black would allow me to freely develop either or both of them if I so want to in Soul Silver, or later in D/P/P once I have the National Dex. So I ask this: is yours a Nidoran♂ or Nidoran♀? I prefer the female (♀) as apparently there is some chance of breeding it to get a male, whereas the male cannot breed a female at all. Further, the Nidoking and Nidorino can still breed, whereas the Nidoqueen and Nidorina cannot; after I breed a few Eggs, if I still don't have a male, I can always breed for one. Even so, they are separate Pokédex entries, and I do need both eventually. At worst, I can always import to White 2 someday if needed from Gen. IV.
So female first, but if there's any chance at both, what would you like for the second?