Should I install 32-bit or 64-bit Linux?

Answer:

Quote from AMD, the company who created the AMD64-architecture-that-your-64-bit-Linux-is-using.

Use a 64-bit system and stick to the compat layer if you have the need of running certain 32-bit applications.

Is it clear?

More information, see: http://forums.amd.com/devblog/blogpost.cfm?threadid=93648&catid=317