Balrogs: -Immortal -Average weaponry is useless against them -Out of the three specifically recorded Balrog deaths, every one ended up taking the life of the victor in the process (Glorfindel and his Balrog, Echtelion and Gothmog, and Gandalf and Durin's Bane) Dragons: -Mortal, but long lived (Tolkien's unfinished [i]Hobbit[/i] rewrite says 5000 years) -Can be killed with conventional weapons -Out of the four specifically recorded dragon deaths, the victors survived the battle (Turin and Glaurung, Earendil and Ancalagon, Fram and Scatha, Bard and Smaug) My vote does to Durin's Bane.