Oh, are you asking for an extrenal storage?
Then it won't mattter, as the path you choose (USB 2.0, Firewire,USB 3.0, or eSATA) will determine the transfer speed.
Except for USB 3.0, the drives will be faster than the pathway.
I never got my eSATA to work like it should, never got better than USB 2.0 speeds (10-15 MBps).
I haven't tried USB 3.0 yet, as I have no need.
My backups are internal drives, and I also backup thru a Home Network.