Question About Joining The Army?

I have asked this a lot but I still get mixed results. I want to join the Army. (for arguments sake say i smoked marijuana 1 time 4 years ago). Am I eligible for enlistment? Also i was thinking about being in the military for quite sometime (more than 2 years). Also can I join the Rangers if I smoked 1 time 4 years ago? Should I join the Marines instead? I read about enlistment and everything and about receiving waivers and how it varies between recruiters and I know that they vary between military branch and recruiter. Thanks for the help.