It's good that valium worked, but benzodiazepines are addictive and you can become tolerant very easily.
i've been on klonapin for about 5 years and it no longer does anything for my anxiety or manic/depressive episodes.
methadone, as a narcotic, must be even more addictive.
it seems to me that if marijuana helps you as much as the other things you have tried, it is the least harmful.
this is just my opinion...i'm no doctor, but because i am so often prescribed to different pills, i always read about what i'm taking.