Originally Posted by jschiwal
The first one (32 bit pc). Even with an x86_64 processor you can install the 32 bit version.
Moreover, the 32 bit versions are generally less hassle than the 64 bit ones. From what I've heard the 64 bit versions don't give you a noticeable performance boost, and it can be a problem to get some binary-only programs to work - mostly commonly flashplayer is annoying. It is possible, but I think it is fiddly on a 64 bit system.
The only thing which 64 bit give you which you may really need, is the ability to address very large amounts of physical memory.