It appears that the recommendation is to install the safest and most compatible version. There are some programs and even some hardware that work best - or even only - with the 32-bit version, although these are few and becoming fewer.
When I installed Ubuntu for the first time a few months ago, I followed the recommendation, too, and so got the 32-bit version. After awhile I got to wondering if I could have installed the 64-bit version, so I downloaded and installed it. I found the 64-bit version to be just a bit faster and everything ran on it, so I've stayed with it.
However, I also found that one piece of hardware, the Linksys AE1000 access point, did not have a 64-bit driver and the 32-bit driver would not work with it. For me it was no problem, as I had an ethernet connection on my desktop and didn't need the wireless access point (I had installed it with the 32-bit version just to see if I could get it to work). But if I had been using a laptop that needed that particular hardware, I would've had to go back to the 32-bit Ubuntu. So I would suggest trying the 64-bit Ubuntu, but don't delete the 32-bit version until you're sure the 64-bit works.