The muscle of their respective teams, these two hate each others guts and aren't afraid to show it. When these two meet there's more testerone flying round then a Mr Universe contest. I've enjoyed the fights between the two massive behemoths and they've generally seemed to be pretty evenly matched so far. Breakdown took out Bulkhead decisively in Deus Ex Machina but Bulkhead replied by getting the better of his opponent (and Knockout) later in that same episode and again in Speed Metal (albeit this time with some help from Bumblebee) and their most recent fight ended in a stalemate with all involved being blown away in the Artic, and Breakdown being left possibly stranded by his fellow Decepticons. I think it's pretty close but I'm going to give the edge to Breakdown because generally he seems to be outnumbered when facing Bulkhead who usually has a buddy with him, but he still manages to hold his own most of the time. But Bulkhead is strong in his own way, with not an ounce of hesitation, he is willing to throw his body on the line to protect his friends or doing the right thing, perhaps that does make him stronger than Breakdown in a way? Afterall strength is not just measured in phsyical attributes.