I have used Nucleofection with great success. But the only downside is you need the instrument. https://www.lonza.com/nucleofection. I have also transfected with Lipofectamine LTX with 10-20% efficiency. I transfected the monocytes in Opti-MEM and LTX and then differentiated them (PMA) after 12 hrs. In my hands, macrophages were less transfectable. I did not attempt to make a stable cell line though.