Thought I'd throw in a vote for MindManager. Its fast, simple, clean and clear maps don't get in the way when you're brainstorming or organizing. I find NovaMind's interface unappealing and the maps somewhat childish as well. As a designer, all that is very important to me.
That childish, whimsical (often ugly) approach is one of the things that turned me off mind mapping in general when it was initially developed. So, technically, Novamind is truer to the original source (Tony Buzan) but that's its weakness as far as I'm concerned.
I would love to be able to easily get content out of OF and into MM, though. I tend to accumulate Someday/Maybe's in OF then want to export them to MM to keep my OF database manageably lean. It's a pain in the butt, so far. If anyone has a suggestion, I'd love to hear it.
I tried the Applescript posted here
http://web.mac.com/robinfrancistrew/...ioutliner.html
but it ended up creating many, many duplicates in the resulting OO document, requiring lots of hand editing.
I wish OF would just export to OO format natively. That would simplify so much.