Well both drives come from very reliable companies. I've just read soo many good things about the M4, as wll as the 320 (besides the 8MB bug lol).
If I were to build a system today - I would get the M4. Currently I own an OCZ Vertex 2 and have been happy with it.
But it's up to you. If you really prefer Intel - go with it. But the Crucial is a pretty solid SSD right now.