http://complement.sourceforge.net/compare.pdf 
 
This article present comparison of strings (and some iostreams features) implementation in STLport (v. 5.0.1) and libstd++. This tests also can help to answer on questions: is it strings copy algorithm with constant complexity better than algorithm with linear complexity? What allocator is better? This comparison is done on the base of STLport strings, ropes and libstd++ strings. I expect that this results will help to make decision between STL implementations as well proper choice of strings implementation.