When starting the game, I was under the impression that you could mount any overridden Machine, regardless of size (like riding a Behemoth in Shadow of Mordor). However, out of the handful of species of Machines I've overridden, I've only been able to mount the Striders. When I overrode Watchers or Sawtooths (Sawteeth?), I wasn't given an option to Mount them.
Are you able to ride multiple types of Machines or are Striders the only mountable ones?