This is a really good question but there is no really good answer. The research that's been done and from talking to people we find that you can't compare. Addiction means that you no longer have control of your drug use. People think you can drink beer or marijuana because they are not too bad. People who have been addicted to either will tell you that the loss of control is devastating.
Nobody knows how fast or slow addiction takes place.
Like fire, if you play with it, sooner or later you get burned. I refer you to the NIDA web site. There are slides showing the effects of several drugs on the brain. Marijuana has long lasting affects on the brain. Alcohol causes dementia.