Which one is better and cleaner from an implementation stand point so that one can recommend as a study guide? The way i see it, one can really learn a lot by just looking through those C library(with C++ things get ugly imho) implementations and toying with them, since they are rather simplistic in design and concept. I am expecting non-biased answers from people who have looked through both implementations.
For people who didn't know, most of Microsoft's implementation of the C/C++ libraries is available for debugging purposes. You can find them in your Visual Studio installation folder under VC\crt\src\. Eg. for VS2008: c:\Program Files\Microsoft Visual Studio 9.0\VC\crt\src(assuming you installed a copy in c:\Program Files\).
I always wondered why C++ STL implementation used by Visual Studio is so hard to read, so I cannot recommend it for sure. I don't know about others implementations. e.g. STLPort