methodone maintenence or heroin maintenence, which is better.

methodone maintenence or heroin maintenence, which is better?

coz i have heard of people who were on methodone who switched to heroin
because methodone made them feel sick or something.  why do doctors
prescribe methodone anyway?  why not just use heroin?

is the only reason doctors use methodone because it's illegal for them to
prescribe heroin?  in otherwords, are the laws on this tying the doctors
hands from what they really want to be doing?  that possibly being
prescribing heroin.