The Twelve-step program is both the oldest and among the most well-known programs in the modern recovery moment, and has helped thousands and thousands of people from all over the world work through their addiction and successfully journey towards sobriety. Using a model of peer support groups who work through a program together, it helps addicts seeking recovery recognize their need for help, surrender to a "higher power" (which can be either a form of spirituality, or the communal connections within the group itself), and get the strength to pursue continued healing for themselves and reconciliation to others hurt by the addiction.
The program began with "Alcoholics Anonymous," specifically for people with an addiction to alcohol, but it has since expanded to deal with many other addictions, including "Narcotics Anonymous," that deal with drug addiction more generally. Many people may be addicted to both alcohol and other drugs, and so might feel they would benefit from either an AA or NA meeting.
Although basically similar, the nature and goals of those organization are a little different. Here are some of the things to consider to help you decide which organization is right for you.
The nature of addiction itself is the key thing, more than the substance itself
If you have had issues with both alcohol, and another drug of choice, or even multiple addictive drugs, you are not alone. A 2001 study led by G.L. Staines published in the Journal of Addictive Diseases found that of 248 people seeking treatment for alcoholism, 64 percent also had a drug addiction.
People who develop addictions do so because of a complex combination of genetic factors, environmental factors, and individual ways of coping with those factors. If you struggle with having an addictive personality, it often matters very little what exactly you became addicted to.
In fact, focusing too much on avoiding one substance may simply cause you to transfer your addiction to something else, like a perscription drug addict who turns to alcohol to "take the edge off" their attempted withdraw. Instead, you focus should be on the root causes of your addiction, and making general, sweeping lifestyle changes to living a totally sober, and healthy life.
For this reason, it may be helpful to start with the group meeting that matches your initial or strongest addiction, but you need not stay there. Any group that is truly focused on recovery from an addictive lifestyle will be life changing.
A subtle, but significant distinction
Alcoholics Anonymous, as the name would suggest, is centered around alcohol addiction, although it member's also strive for total abstinence from all mood-altering and addictive drugs. Narcotics Anonymous is centered around addiction more generally, and will center around the difficulties related to abusing substances in all its forms.
Various AA meetings may be more or less open to discussing your issues with other drugs, and it is helpful to everyone if you respect the wishes of those who view your struggles with other drugs as a distraction away from "the core program."
Every group has it's own feel to it
Both AA and NA groups are completely peer led, and only loosely supervised by a national organization, each group is allowed to develop its own feel to it. Different people may have different experiences of addiction, and what works for one type of person may not work for everyone.
In most places on earth, you will likely have a choice of a wide variety of AA and NA meetings, and you need not feel guilty about visiting many types of groups to see which one is the most helpful to you. Pick a group that has people with whom you most feel safe, or those whose stories most match yours, so that you can truly commit and get the maximum benefit from the program.