I just download each one, and choose x64 if I'm running a 64 bit OS. It's really based on what you're using or want to use.
Also make sure you download and install the prerequisites for this profile too (links found on page 1):
Prerequisites
Download and install:
NOTE: This is VERY important! Can't stress this enough.
Download Microsoft .NET Framework 4.5.1 (Offline Installer) (REALLY important that you have the latest one!)
Download Microsoft Visual C++ 2010 x86 Redistributable - 10.0.40219
Download Microsoft Visual C++ 2010 x64 Redistributable - 10.0.40219
Download Microsoft Visual C++ 2012 x86 and x64 Redistributables 11.0.61030 (Installers have the same filenames as the 2010 redistributables. Careful not to overwrite them.)
Then also ensure you're fully updated on windows, using windows update, and everything should work great.
Its not based on what OS you are using.
I have been using 64 bits OS the last 5 years, and I only had the x86 version, so there is something that dont "click" here.