When I was a student, I joined the AANP. I enjoy the daily e-mail (smartbriefs) sent, it keeps you current with many issues. My friend was a member of the ACNP, did not receive any informational e-mails.
I did not, however, obtain my certification through the AANP, went with ANCC, much easier to deal with.
You can get the smart briefs free, even if you are not a member. AANP is very difficult to deal with - I was certified by them as a Adult NP a few years back, which was not necessarily a smooth process (lost my transcript twice) and I recently went back and got a Post Master's FNP and after 4 MONTHS I still do not have authorization to sit for the FNP exam (lost 2 transcripts twice). Communication is impossible- to voice mails, emails, snail mail, 20+ calls. I will never give them another penny. It will be beneficial to you to be a member only to get a discount to sit for the exam and get a discount to the conferences. I'm sure others will disagree, but I have had (and still having) a very bad experience with them. There is a reason why they have a "F" score on the BBB.
I joined my state NP organization, rather than a national one. I felt that this membership would be more relevant to my day to day life, and it allowed me to get involved in state legislation that could directly impact my practice. Plus, it had the added bonus of being the best source of job openings for NPs in my area! I may join one of the national groups at some point, but for now I'm staying local.