Firelord wins. Nimrod, as advanced as he is, is still a sentinel, which means he's still artificial. Therefore, he can overheat, and i doubt that he could withstand the maximum heat of 100,000,000 degrees that Firelord can put out.
MER
MERCILOUSALWAYS METAL
And yet there are still those who beleive Spidey versus Firelord was a ligit fight.