Phobos' gravity well
With no gravity well to speak of, Phobos would be safer and cheaper to land humans on...
I've heard some wags "in the biz" remark that a spacecraft wouldn't so much land on Phobos as dock with it.
Given Phobos' low escape velocity (a person could easily throw a ball up fast enough that it never comes down) I wonder if these things could take a run-up at a suitable slope (e.g. Stickney's inner wall) and launch themselves into Martian orbit?
About the time that the NEAR Shoemaker probe was finishing its mission at asteroid Eros with its famous daring "bumpdown", Eros' gravity was described as so weak that an astronaut standing on its surface would have to avoid jumping so as to not accidentally launch himself into orbit. It's also been suggested that astronauts visiting bodies like Phobos (or Eros) would have to be equipped with modified mountain climbing gear -- spiked overshoes, carabiners, cables, etc. -- as walking in a normal fashion would be nearly impossible owing to the weak gravity.