armhf is a new Debian architecture with a calling convention that passes floating point values in floating point registers, so it should be faster than the old Debian armel on devices with hardware FP units.
My initial installation was based on a root filesystem that Konstantinos Margaritis of Genesi made available (see this thread). Unfortunately, unknown to me, this image and the repository at debian-ports.org that it referred to were considered "proof of concept / pre-release / absoutely no guarantees", and a subsequent attempt to update led to me almost bricking the device because apt deleted the dynamic linker. This episode has rather dented my trust in Debian, since I thought this sort of package-incompatibility disaster was exactly what apt and dpkg were supposed to prevent from happening.
I'm not sure what to recommend as an alternative, since (as far as I am aware) there is no support for this board in debian-installer nor is there any "official" root filesystem image. The best choice is probably to debootstrap from whatever Freescale supply on the SD card.