I run 64 bit on the desktop I have that is capable but my 2 laptops are 32 bit only so they get 32bit
Once my hardware upgrades to 64 bit I would run just that. I really like it. I do not even go multilib, just 64bit pure.
I strayed from Slackware for about 6 months but came back to stay..... it runs so well, just love it. And, the new documentation project site is totally awesome and has helped me a great deal already.