Both are good, i prefer methanol, because its elimination is easier that water, and both can extract similar compounds, if you want to separate the extract by CC, also is easier with MeOH. The compounds that you can find are polar metabolites (flavonoids, phenolic compounds, alkaloids, etc).

I agree with Miguel, I also usually MeOH; after that, if it is needed  you can fractionate te MeOH extract using hexane, CH2Cl2, and acetone. With MeOh you can have almost all metabolites (for metabolite profiling in plants usually I used MeOH); but for decoction I think you should only water.

If you are interested in an specific class of compounds, you would use a solvent with an specific polarity. But if you want extract as many class of compounds as possible, using a mix MeOH/H2O is a good idea. You can also replace MeOH by ethanol, which is less toxic. 

I've been working by both maceration and using soxhlet apparatus, the higher yield was from maceration while soxhlet was tedious and slow but it works efficiently with light solvents such as petrolium ether and methylene chloride. Decoction I think would give high yield but may cause degradation of some compounds.

For the solvent I used Methanol then fractionation 

Better use MeOH.  Most of the compounds   soluble in MeOH 

Thanks for your answers, they are very important.

Check these links and publications:

http://www.slideshare.net/rahulbs89/extraction-of-plant-contituents

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

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

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

https://www.researchgate.net/post/How_can_I_separate_pure_product?_tpcectx=profile_answers

https://www.researchgate.net/post/On_what_basis_can_I_choose_a_solvent_for_soxhlet_extraction_technology#55409e65f15bc7284e8b45fe

https://www.researchgate.net/post/What_is_the_difference_between_Soxhlet_extraction_and_extraction_by_normal_refluxing_method?_trid=55409f14f079ed3f058b456c_

Thank you very much Prof. Rajeswara Rao.

You could also use a ''Vacuum flask'' that you can connect to to the water tap.

It allows to extract much more filtrate, and enhance the yield extraction

Take care!

I prefer to use methanol and Rabia just told you the way to get a very good extraction, but any way some time you can try various methods using small quantity of plant and try by yourself the best for your plant.

For separation and purification I recommend you to use gel filtration such as Sephadex LH20.

I want to thank every one who send an answer.

Best regards

Souad

In my view methanol is usually the best solvent for plant extraction as most phytochemical constituents are dissolved in it

Start with methanol using soxhlet to get methanol extract and marc remained after methanol extraction is macerated with water to get water extract. Then combined both the extract to get total yield. Which contain both polar and non-polar chemical component of your plant.

Depending on the nature of the metabolite that you might want to extract, methanol either pure or 70% /30% solutions may be used, which you may have to optimise, according to your tissue type, moisture status etc. Methanol is generally the best solvent for use with secondary metabolites. Even though soxhlet is a good technique, but if you might want to save on time and effort , ultrasonication/ microwave extraction may prove quite advantageous.