So I loved the "most annoying companion sayings" thread, so I felt a best companion sayings thread is also warranted. Forgive me if this has already been done, but it is all in good fun.
My favorite companions is M1-4X, and he has some great sayings.
The top of the list for me is:
"Thus to all who threaten galactic liberty!" (after killing an enemy)
and
"My armored chasis is impenetrable to your touch, no matter how repetitive." (when clicking on him. I laughed so hard the first time I heard it)