Finding which files the migration assistant failed to transfer
Open a terminal and execute:
diff -qr /Volumes/newharddrive /Volumes/oldharddrive

you have to change the names of the hard drives (or directories) according to your setup.
diff -qr /Volumes/newharddrive /Volumes/oldhardrive | grep ' differ'

is a variant to reduce the output clutter.
You can redirect the output from the terminal to a text file for easier reading:
diff -qr /Volumes/newharddrive /Volumes/oldhardrive &gt;compare.txt