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S12a. Which interpretation of quantum mechanics is most consistent?
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The most widely prevailing interpretation is probably 
''shut up and calculate'' - trying to stay clear from the 
interpretational problem, the ''blind alley from which nobody has 
yet escaped'' (in Feynman's words). Probably it was Mermin who coined 
the name of this non-interpretation, although it is generally 
attributed to Feynman. See 
   N.D. Mermin, Could Feynman Have Said This? Physics Today, May 2004,
   http://www.physicstoday.org/vol-57/iss-5/p10.html
But even this non-interpretation needs some core to make the results
of the calculations applicable to reality....

Among the traditional interpretations, the statistical interpretation
discussed by 
   L.E. Ballentine,
   The Statistical Interpretation of Quantum Mechanics,
   Rev. Mod. Phys. 42, 358-381 (1970)
is the least demanding (it assumes less than the Copenhagen 
interpretation and the Many Worlds interpretation) and the most 
consistent one.
For a discussion of what the Copenhagen interpretation entails
(different authors use the term quite differently), see
   HP Stapp
   The Copenhagen Interpretation
   American Journal of Physics 40 (1972), 1098-1116.
For a discussion of the Many Worlds interpretation, see
   On the Many-Worlds-Interpretation
   www.mat.univie.ac.at/~neum/manyworlds.txt .

The statistical interpretation explains almost everything, and only 
has the disatvantage that it explicitly excludes the applicability 
of QM to single systems or very small ensembles (such as the few solar 
neutrinos or top quarks actually detected so far), and does not bridge 
the gulf between the classical domain (for the description of detectors)
and the quantum domain (for the description of the microscopic system).

In particular, the statistical interpretation does not apply to 
systems that are so large that they are unique. Today no one disputes 
that the sun is governed by quantum mechanics. But one cannot apply
statistical reasoning to the sun as a whole. Thus the statistical 
interpretation cannot be the last word on the matter.


The many world interpretation has the apparent virtue that it 
can be applied to individual quantum systems and hence to the
universe as a whole. But it suffers from other severe defects
that rules it out as a viable alternative, discussed in this FAQ
under the entries ''Circularity in Everett's measurement theory'' and
''On the Many-Worlds-Interpretation''.
People who prefer many worlds do it apparently mainly because it gives
a meaning to the state of the universe as something objective,
not because it solves the interpretational problems.

For my own, ''thermal interpretation'' of quantum mechanics, see
the FAQ entry ''Does quantum mechanics apply to single systems?'',
and Chapter 7 in the book
    Arnold Neumaier and Dennis Westra,
    Classical and Quantum Mechanics via Lie algebras,
    Cambridge University Press, to appear (2009?).
    http://www.mat.univie.ac.at/~neum/papers/physpapers.html#QML
    arXiv:0810.1019