For all most all of us out there: 64 bit. Why? Again for all most all of us out there: RAM. 32 bit is limited to a maximum of 3.5 gigs of RAM. While the 64 bit is only limited to the RAM capacity of the mobo. More RAM equals more speed in the most basic of terms. I run 7 Ultimate 64 bit with 8 gigs of RAM, while my mobo RAM maximum capacity is 16 gigs of RAM.
As far as the stability issue....That is mainly a myth now. Yes, when the 64 bit OS was first introduced some years back it was buggy and stability was an issue. Now in the modern day you have no worries from the OS stand point.
I recommend the the 64 bit and go Pro. See comparison chart.
Compare Windows - Microsoft Windows