Hard drugs get you strongly and quickly Physically Addicted. Do not confuse that with a mild Psychological addiction. Many slashdot comments are getting this wrong. But not all addictions are the same
Many legal drugs will get you addicted. But that's why we control those substances as well. A large part of being on the federal schedule is that the illicit drug has no real medical use ( or so they say ). So it's not about which is most addictive, but rather what's addictive while arguably also having no medical use.