I have the basic understanding that ね is generally more formal/feminine and な is generally more informal/masculine. I was told that you tend to use ね as an emphasis if you are a) a female yourself or b) are addressing a female, regardless of your gender.
But say you were a male addressing a group of friends of both genders. Something like: ひさしぶり！Would you use な or ね at the end of the sentence for emphasis?
As was pointed out (probably by Tsuyoshi Ito) in an answer/comment to another question on this site (which I cannot find right away), the gender connotation of な and ね depends on whether it is attached to a clause or a noun. When they are attached to a clause, the connotation is not that strong, and can usually be dismissed. When they are attached to a noun, the connotation is strong.
久しぶりだね (gender neutral, or very slight feminine connotation)
久しぶりね (feminine)久しぶりだな (gender neutral, or very slight mascline connotation)
その本がな、... (mascline in Tokyo dialect, gender neutral in Kansai dialects)
久しぶりな (somehow, not completely ungrammatical but unnatural to directly attach な after a noun without a particle)
I guess you mean ひさしぶり. And to answer your question, for a group a friends, I would use 久しぶりだな no matter their gender(s).
There is the gender factor of course, but there is also much more. It depends on your gender, your speaking level, your social position, your personality, the social position of your listeners, etc.
It could be the same as debating when to use わたし、ぼく、おれ etc. Some men in very manly, high positions use わたし or ぼく.
The same goes for ね／な: there is no universal rule. It's best to listen to what people say around you and define what you think fits you the most.
PS: I think I am correct in saying we are not talking about the specific meaning of な in どうかな and similar phrases in this question.
