I have many doubts about this point:
-Who is recommendable to prepare this letters?
-Are essential in the process or only a formal requirement?
-It should be a high position recomender or it does not matter?
-Its a key point in the admitted -process?
regards.

Of course it is essential, as the letters are required by all schools and used as a measurement for your qualities.

Preferable are of course letters from the best law professors you can get. I would recommend getting letters from professors, except when you've been at work for several years and you've lost links with professors.

The prestige of the professor can matter also, so I would recommend getting letters from the best professors. Judges in high courts, known practitioners, ...

@ Santa...

hi; Am applying for LL M coming season ..; Have almost consolidated all my reco letters. Santa, I would be obliged if you kindly elucidate on "Prestige of the professor" (I have one from a prof who has been teaching at a well known Law school since '83 and another one from a solicitor/Partner of a law firm that I worked with. Is that good enough?

I only ask you to explain Sir, because my take is that because of the information asymmetry, it might be at times difficult for the law schools to "know" our recommenders. (discounting the cases where applicants have provided recos from say, The Chief Justice or sth.)

If it comes to choosing between relatively less known "referencers" who know you well and well known "referencers" who only had a cursory role to play, what would be your advice? Thanks a lot...