Halacha sheilas should generally go to a Rav. There are almost no women who are qualifed to answer halacha sheilas, since there are very few women in the world who have even studied halacha from the sources. And it is doubtful if any of the Rebbetzins you know have.
For personal issues, it’s generally better to speak to a Rebbetzin.
For hashkafa – either one. If it’s a question that’s more personal and requires someone with intution and sensitivity, a Rebbetzin might be better. If it’s a question that’s more intellectual and non-personal, a Rav might be better. But both of those last statements are generalizations, and it would depend on the Rav and Rebbetzin in question.