One of the fastest way to copy files is use robocopy as pointed by Pyrolistical in above post. its very flexible and powerful.
If command doesn't work from your dos prompt directly then try with powershell option like below example.
Must Check the documentation for this command before using it "robocopy /?".
powershell "robocopy 'Source' 'destination' /E /R:3 /W:10 /FP /MT:25 /V"
/E - Copy subdirectory including empty ones.
/R - Retry 3 times if failed.
/W - wait for 10 seconds between retries.
/FP - include full path name in output.
/MT - Multi thread.
/V - verbose output.