[Update: Big news. FreeMind released its first 1.0 version on 16 October 2013, after years in beta and multiple Release Candidates.]
I took a brief look at both of the latest versions.
Freeplane remains my preferred tool of the two. I find the interface more usable, and I like the fact that the file format does not appear to have changed, and there is a 64-bit version for those running 64-bit Windows.
I have many old .mm files and when I try to open them with FreeMind, it tells me it will convert them (with no going back), but then presents a map with a single central topic stating that there’s a parsing error. Freeplane opens the map without problem.
The original FreeMind format became an industry standard with many mapping tools being able to import and export .mm files, so it is a shame this change has not been handled with full backward compatibility.
One advantage of both FreeMind and Freeplane is that mapping from the keyboard is fast and easy. Good for quick note taking or catching ideas without interupting the flow when brainstorming.
I’m working on a review of ThinkComposer. This is a tool with capabilities for making visual models and diagrams of many types and is taking a while to work through.