Number 1 - Bite Force

Bite Force is the dominant competitive fighting robot of all time. Its lifetime record of 26-1 (.963) in Battlebots, and its many top 50 victims (including Tombstone twice) are a testament to its dominance. In season 1, Bite Force sported clamping jaws, and it used them to go 5-0 and win the Giant Nut. It debuted in the next season with a vertical spinner, but lost in the third round to an ax swinging robot called Chomp. It won the consolation rumble at the end of the tournament, however, and was a favorite coming into season 3, when it started a streak of 16 straight tournament wins, capturing two more Giant Nuts in the process. It also went 2-0 in an exhibition tournament in Las Vegas. To the surprise of many, Bite Force did not return to defend its title in season 5, and another vertical spinner, End Game (which Bite Force knocked out in season 3), took the crown. Bite Force hopes to return next season and defend its reputation as the greatest combat robot of all time. 

Number 2 - Tombstone

Tombstone is probably the most feared combat robot of all time. Its devastating horizontal spinner has slaughtered the greatest Battlebots in the world. Its lifetime record is 21-8 with 18 knockouts. Its victims include top 50 members Witch Doctor, Bronco, Brutus, Beta, Yeti, Bombshell, Minotaur, GIGABYTE, Whiplash (twice), DUCK!, Tantrum, Lock Jaw, SawBlaze, Gruff, Quantum, Slap Box, and Mad Catter. It was the runner up in season 1 and the champion in season 2 (the above fight is the title match from that season, believe it or not). In season 3, it went 4-0 in contesting matches but lost a close one to Bombshell in the tournament. It went on in season 4 to make the quarterfinals, the Battlebot that took it out in season 1. In season 5, however, Tombstone went 1-2 in contesting matches, the result of the worst luck and seemingly simple mechanical problems. It made quick work of Mad Catter in the tournament but lost a judges' decision to Black Dragon in the next round. Because its design is so simple, and because more modern Battlebots are becoming more advanced (not to mention the fact that most everybody designs his robot specifically to contrast Tombstone's big spinning blade), the "undisputed master of disaster" has fallen out of fashion with a big number of fans. When it returns in season 6, I expect it to be one of the favorites to win the whole thing. It has proven itself capable many times in seasons past.