M4 has larger screen at higher resolution and it has a better video card. Fujitsu is smaller, much lighter, and has the indoor/outdoor screen option. Both are from excellent companies that have been dedicated to tablets for a long while.
THe final answer depends on how you plan to use the tablet. Give us a bit more to go by and more people are going to chime in. Personally, I go for portablility and need a light tablet. But, if I was to get a second, I wouldn't hesitate to get the M4.