I believe that modern medecine is probably the most effective medicine in most, but not all instances. Most medicines were derived from so-called "herbal" medicines, where the active part of the herb is isolated from the rest of the plant.
One of the disadvantages of using herbal medicines is you get the whole plant - active compound and all - and this might not necessarily be good if someone has an allergy to a certain part of the plant or if there are toxins in the plant. I still use some herbal medicines myself, but I am careful about it.
An interesting thing about medicine is the placebo effect - even if the medicine doesn't have any effect at all in the body, if you take a medicine and THINK it will make you better, chances are it will. I don't think scientists fully know why yet. This might be what's behind a lot of "traditional" medicines.