From an economic point of view, I would consider the extraction (solving in nonpolar solvents).

I agree with Dr. Andriy V. Proskochilo.

In my former research center, we have always used solvent extraction followed by distillation.

Greetings!

In my view, the best method is solvent extraction method.

After solvent extraction, you can perform simple column chromatography for purification purpose.

I believe there were papers recently in JMAP relating to this.  See www.acmap.org and click on Journal.  Free downloads from journal.  Also note that we have an annual meeting coming in June 2015 in Spokane WA and will be asking for abstracts submitted for presentations.  Carol Stiff, Treasurer ACMAP and Co-Chair of 2015 Conference Committee

thanks a lot, please inform me

Solvent extraction in Soxhlet is the best method for oil extraction from plants.

you can take benefit from this paper

http://nopr.niscair.res.in/bitstream/123456789/16846/1/IJTK%2012%282%29%20272-276.pdf 

As per my view, medicinal oil may be either essential or non-volatile. Therefore, for volatile/ essential oil solvent extraction followed by distilation will be better as suggested by one of the previous researcher. For non-volatile oil, only  solvent extraction may be preferred.    

Hydro distillation would be the best method if the oil to be extracted is non volatile otherwise solvent extraction or accelerated solvent extraction could be used. The solvent used in this case is important

Pressing : Commonly used when the oil is extracted on commercial scale with the availability of resource is sufficient. Like Extraction of Mustard Oil.

Heating is used when the oil is non-volatile using hydrodistilation. Hydrodistilation is ecofriendly.

Solvent extraction can be used but not ecofriendly and costly.

So mode of extraction will depend on the nature and quantity of sample.

if we have poison agent in oil which one is better?

Dear Mr. Saeid Davazdahemami! In your case it would be better to use extraction in a closed system. 

Dear Dr. Vinesh Kumar. Do not jump to conclusions. You are mistaken if you think Solvent extraction is not ecofriendly. Using modern technologies of extraction, such as supercritical fluid or liquefied gas extraction, allows to refute the assertion of harmfulness of Solvent extraction. At the same time, I agree with you that mode of extraction depends on the nature and quantity of sample.

Regards.

Hydrodistillation with clevenger's apparatus will help you.

I also agree that the method used is determined by the nature and amount of the sample.

I have found hydro-distillation using the Clevenger-type apparatus, a suitable method for extracting essential oils from leaves.

Different extraction techniques, extracts oils with different physicochemical properties. Hydrodistillation and steam distillation (although here, not only yield but composition can vary) produces the 'essential oil' (basically terpenes), which m/z (mass to charge ratio) generally not exceeds 300 Da. Cold press usually do not extracts essential oil components, but non volatile substances, reaching m/z higher than 300 Da, but also potentially with medicinal properties. I would say, there is not a "best" method or technique, but those which best matches the portion of the plant, which contains the active substances. 

Dear Saeid

Your question appears to have created some kind of ambiguity. There are several methods to isolate essential/volatile/aromatic/ethereal/fragrant oils from aromatic plants. You can view these methods in Vinesh Kumar's thread. These essential oils are extensively used in flavor and fragrance industries. They are also used in several other industries including for medicinal purpose bur rarely are called as medicinal oils.

In India, medicinal oils are extracted in different traditional systems of medicine and are widely used for different purposes. Examples include hair oils of Hibiscus, Eclipta, Bacopa, Mentha species; medicinal oils for arthritis, body pains, skin problems etc. In these oils plant parts of several plant species are used to produce the medicinal oil. In these preparations the herbs are cooked or extracted by heating  mixture of an oil (coconut, Olive etc.) and the herbs (in specific proportions under specific heat conditions) for a specific period of time, filtered and recooked if necessary, re-filtered, cooled and stored before use. You can see excellent videos (Cannabis oil for cancer) on YouTube about some of these medicinal oils.

https://www.researchgate.net/post/What_are_the_techniques_used_for_the_extraction_of_essential_oils_from_a_plant

https://www.youtube.com/watch?v=bH6olqGpFc4

https://www.youtube.com/watch?v=vs66uyiH968

https://www.youtube.com/watch?v=E37RxzsRJ-k