Ironhide was more immediately shocking and disturbing but seeing Ratchet's corpse being melted down was more of a slower, anger-festering tragedy.

Although I gotta admit both mostly made me see the villains as evil more than making me actually sad.

 

Ratchet. He was hunted down, the MEDIC of all bots, and refused to fire on his aggressors, pleading them to stop hurting him. It's only after he's absolutely forced to does he fight back and then Lockdown's callousness happens. That whole sequence, from running Ratchet down and blowing his leg off to his spark extraction is saddening and infuriating, one of the rare scenes that gets to me in any of the movies. Bee's torture scene in the first one sucks but there's a....mean-spiritedness to Ratchet's scene that hits a lot harder.

Ironhide has the shock value but lacks the heart to truly get at you.

 

I just rewatched Age of Extinction the other day and Ratchet's death is pretty upsetting. He's scared, in disbelief, shredded to pieces, and finished off in a really drawn out scene.

 

Ironhide is my favorite bot from the first three but honestly Ratchet's was worse. Putting aside how little attention the movies themselves gave him, they really made him so pitiable in his final moments, alone, wounded, and betrayed, and the later desecration of his body was the final spit on his grave that really drove home the utter contempt he was killed with.