well, it depends on what kind of use you're talking about. the pentium M has a low TDP (makes little heat) and has good battery life, so its good for lappy's and for Overclocking. It has a high IPC, so its efficent, but it has a poor ALU (because its basically a heavily modified Pentium III).
The A64 is (IMHO) the best desktop PCU right now. It has less TDP than anything intel has on the desktop, it has a higher IPC than the P4, and outperforms its competors in a majority of benchmarks. The P4 is still better for video editing (and I guess) multi-tasking, though my A64 has never had a problem. A64s are much cheaper to build/upgrade (at least right now).