Lately I've been doing a lot of professional speaking, and find that I much prefer mind maps to outlines. Probably that's because it's easier to keep yourself oriented with a glance -- the spacial cues are quicker to decode.I also find that mindmaps are easier to brainstorm with -- freer (I liked the comment about them being "airier"). I'm less worried about hierarchy at the beginning.

For writing, though, nothing beats the outliner for making sense of things, checking proportion, flow, structure.