Although most folks probably identify the ATST vehicle more closely with ROTJ (and those pesky Ewoks), the "chicken walker" was actually first glimpsed, briefly, during the Hoth battle in Empire.
And I thought they smelled bad on the outside. Frankly, I've always found Empire's awkward combination of stop-motion and models in animating the Tauntauns to be a little jarring. Why does a creature that looks like it stepped out of a Harryhausen film in the long shots suddenly look like a muppet in closeups?
By contrast, these speederbike models I thought blended perfectly in with the live action shots in ROTJ.
The evil Jabba's Sail Barge, also from ROTJ.
Once again, this is obviously not the one those destructive types at the ILM model shop blew up.