I'm not sure it's the best of its kind.
However, it is pretty good at keeping my contacts & calendars synced on my family's 4 macs and 2 iphones. And for keeping bookmarks synced on the 4 macs and one office PC. For that alone it's worth the money.
As for iDisk, I put up with the many multiple file version problems and super slow syncing... until the day all my files disappeared then synced empty directories to all my macs, with no ability at Apple's end to restore. Good thing I had my own backup!
Then I discovered Dropbox, which:
- is FREE (up to 2Gb storage, which is more than enough for most people's necessary syncing requirements)
- syncs files PERFECTLY and near instantaneously
- gives me growl notifications if I want them
- only uploads/downloads the parts of the file that have changed (saving internet usage and increasing speed)
- keeps multiple file version history
- shows most recent files changes
- shows whether or not a file is in sync (with a tick on the file icon in Finder)
- even runs on PCs (sync Mac to PC if you like)
- runs on my iphone
- has a great web interface if you need to use it online
So it's Dropbox for files, MobileMe for all other syncing.