I also do memorization from the KJV. When President Harry Truman was asked what he thought of the then new RSV he said, "They took the poetry out of the Bible." I must confess that is one reason I use the KJV. Not a great reason, and not the only reason, but one of the chief reasons. Verses are just more easily remembered.
I memorize from the KJV. I study from both the KVJ and the ESV. The reason I use the KJV for memorization: that is the version used in the church (denomination) that I attend. It is the "language of the people" in our denomination.
ESV for both study, reading, and memorization. It just helps to reinforce retention by keeping it the same (although I still consult other translations.)