From what I can tell (from various anecdotes on this site mostly, as I have never had to call CS myself), Nintendo customer service is generally excellent, but with Nintendo being such a small company it can be problematic in some more late-start-gaming areas like Eastern Europe, because Nintendo doesn't really have many offices there.
Sony Customer service seems to be on/off good/average... but it is much rarer than Nintendo that things are fixed/replaced for free, whether in or out of warranty..... but Sony has much wider coverage than Nintendo, so will be better help in Eastern Europe.
MS customer service seems to be usually quite poor, though there are some good cases, but then given some people have to call them multiple times for repeated breaking of X360s there has to be at least some times when they are better.
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Obviously anyone can have a bad/good experience with any of the 3, generally depending on where you are and who picks up the phone at the other end.
