Complex sentence: Choosing the best MCDA/MCDM method is itself a multi-criteria decision making problem, in which the alternatives are the methods themselves and the decision criteria are the various evaluative ways for comparing them.
Split into simpler sentences: Choosing the best MCDA/MCDM method is nothing but a multi-criteria decision making problem itself. Now the alternatives are the methods themselves and the decision criteria are the various evaluative ways for comparing them.