What's the fastest way to get data off Time Capsule and onto an external drive?
If you want an exact copy of the TC drive, the fastest way is to connect the USB drive directly to the TC and use the archiving option in Airport Utility:



Other things to consider:


Transfering data over wire (ethernet) is faster than over Wi-Fi
Connecting the USB drive directly to the computer (than to the TC) gives better results if you use the Finder to copy data.