You want the 64 bits version.

The only reasons to use ancient 32 bits versions are:

• You have ancient hardware not supporting 64 bits^*1.


• You do not have much memory and really need the memory benefits of 32 bit pointers.
  This makes sense when you have 128 MB or similar. Not with 4 GB.

Reasons to use 64 bits:

• There is no more 32 bit (4 GB address space limit, thus you can use more then 4 GB physical RAM without trickery (PEA).


• There is no more 32 bit virtual address space. (Not just used for programs, but also for mapping files, or mapping a videocards memory into normal address space. (
  try mapping a modern 6 GB videocard into 32 bit address space.)

Both of these will come in very handy if you later decide to expand your system without doing a complete reinstalation.

As to the memory advantage for 32 bit. Yes. 64 bits programs are slightly faster. 64 bit mode also unlocks additional CPU capabilities. Both roughly cancel each others advantages resulting in an equally fast system.

^*1 Ancient. Or older really low end hardware. E.g. first generation Intel Atom CPU's.