Cloakbot : All units widely used. But maybe the Imp (not the IMPaler), because it's a very specialized bomb unit.
Shieldbot : All units widely used. PARTICULARLY the bomb one.
Spider : All widely used.
Rover : All widely used, but maybe the Crasher (AA)
Tank : All widely used.
Jump : All videly used.
Planes : The sparrow. Why build a Sparrow when you can build an Owl ?
Gunships : All widely used.
Boats : The cuter (no damage) and the corsair (too fragile, not enough range) are rarely seen.
Amph : I rarely see the LImpet (slowing bomb)
Striders : All widely used. Since some time, even the Detriment.