I, too, would prefer to answer your question *after* you have defined
the term 'best', however, I use Intel's compiler suite with Linux and
Intel CPUs, since they create very fast performing executables. On the
other hand, I prefer the XLC compiler with PowerPC and Visual-C++ with
Windows for the same same reason. Finally, if I had to create a code
with maximum portability, I'd prefer the GNU compilers.

Sincerly
Sascha Tayefeh