I was mostly Cass, too, with Rex as my "non-humanoid" companion. Mainly because I hadn't found ED-E until the late-game.

Specifically, the first time I met ED-E was in Lonesome Road. So when my time in the Divide came to its conclusion, and Divide ED-E went off to Navarro, I went and sought out Mojave ED-E, since Divide ED-E had transferred what he'd learned to Mojave ED-E. It was like an old friend walking their own road, but leaving a piece of themselves behind with you.