Either one one of the x86 derivatives without kfreebsd - the 32 bit i386 or the 64 bit AMD64 (intel uses a compatible architecture called EMT64, but since AMD was first to market, many refer to it as AMD64 - the correct generic name is x86-64) would do, practically speaking - the 64 bit x86 architecture is backward compatible with the 32 bit architecture. This would install the good, stable well tested linux kernel
The kfreebsd alternatives use a freebsd kernel with debian userland tools. Its shiny if you want to play with BSD things in a familiar environment but not what you're looking for. ia64 (aka itanium), S390 (a mainframe platform) and power PC simply won't run, since they are fundamentally different architectures.
That being said, if you have, or want to max out the memory, you have to go for the 64 bit architecture (there's workarounds but don't bother). If you have i386 specific applications, you should be covered using the compatibility libraries, you should probably need some form of ia-32-libs package to run it on 64 bit.
All that taken into account, AMD64 bit is the better option