Bumblebee. He's the next invincible mass-slaughtering Autobot after Prime. You know he won't get killed (damn it).
Jetfire. Though Ironhide might be able to manage too. But Jetfire seemed like he was close to Optimus and Megatron level power, with how he slaughtered Mixmaster in seconds. And Jetfire was in poor condition at that too.
Seriously...how many more people are going to mention Wreckers? Question is "Toughest bot" not "Toughest bots".
Bee managed to survive all 3 movies, he killed almost as much as optimus, and i mean just look at his battles.
Obviously Bee. Bay would probably make him kill Sentinal, Megatron, hell, maybe the Driller if he got his way. Thank god he didn't...