Block copying Carbon Copy Cloner normally operates on a file-by-file basis, but when certain conditions are met (for example, both the source and destination volumes must be locally attached and be able to be unmounted), the utility can perform a block-by-block copy, which is faster for an initial backup. (Updates to existing backups are always file-by-file, which is faster for that purpose.)
Honorable mention: ChronoSync
Though SuperDuper and Carbon Copy Cloner are my favorite drive-cloning tools, a third backup app, Econ Technologies' $40 ChronoSync (4.5 mice) earns an honorable mention here. As its name suggests, ChronoSync is primarily a Mac-to-Mac sync tool, but it also includes an extensive set of backup features, including the capability to make bootable clones. Like Carbon Copy Cloner, it can even clone to an external drive connected to another Mac on your network (as long as you install the $10 ChronoAgent utility on that Mac). Also like Carbon Copy Cloner, it can move changed and deleted files to an archive folder on the destination; and like both Carbon Copy Cloner and SuperDuper, ChronoSync supports incremental updates, scheduling, pre-/post-run scripts, and the use of disk images as destinations, although you must create those images manually in Disk Utility.
On the downside, ChronoSync lacks special features such as SuperDuper's Sandbox and Carbon Copy Cloner's Recovery HD cloning; and although it has a massive array of options you can configure, it's not quite as easy to use as my top choices. However, it's still an excellent all-purpose choice for syncing, backups, and cloning.
For making a clone and regularly updating it to reflect changes to the source volume, I could use SuperDuper or Carbon Copy Cloner interchangeably — I have no reason to prefer one over the other. However, given my particular cloning needs and preferences, I find myself using Carbon Copy Cloner most of the time.
For one thing, I like to encrypt my clone backups using FileVault, and for that task I appreciate Carbon Copy Cloner's Recovery HD support. I also like the safety net of being able to archive older and deleted files while cloning (although I still maintain separate versioned backups). I tried SuperDuper's Sandbox feature with the beta version of Yosemite, but while it's interesting in principle, I found that my own usage patterns don't benefit significantly from that setup. And although both apps offer scheduling, a scheduled task in SuperDuper runs, at most, once a day, whereas a task in Carbon Copy Cloner can run as often as once an hour. (To get multiple runs per day using SuperDuper, you must set up a separate task for each occurrence.) Finally, although I can see the logic in how each app presents options for things like deselecting files and deleting files on the destination volume before cloning, I find Carbon Copy Cloner's interface to be closer to the way I think.
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