how to choose the library to include in VC

The vcvarsall.bat that does setup de build environment let you choose between x86 | ia64 | amd64 | x86_amd64 | x86_ia64.First option is obvious for 32bit, but the question is: what would be the optimal option between the other 4 if you want to build for 64bit and you want to run on all 64 bit machines.Let say that you don't have time/resources to make 4 builds for 64 and you have to choose only one of them?

32/64 OS building for 32 => x8632 OS building for 64 => x86_amd6464 OS building for 64 => amd64And you can ignore the other options because Itanium does not have a real market share.