So many Robots

[DOMON KASSHU!]

The leviathan was an awesome robot there. I really liked that giant eel thing.
War.

[Big Duo Enthusiest]

The giant eel thing was cool. One of the three creatures that were acualy organtic and battled Big O. The other two was the cat from the episode Missing Cat and the Three Headed version of the Eel.

Hey, in the Manga, there was an electric mosquito and during that manga, Big-O had an extra pair of arms with electricity conductors. Why wasn't that used during the fight with the three headed electric eel? That would have been kick but, even if Big-O became four armed instead of trading arms.

[DOMON KASSHU!]

Didn't read the manga, but the three headed eel thing was awesome. The first eel still beats it for originality and coolness, however.
War.

[The Final Negotiator]

I had to vote Big O for three reasons:

1. The piston punches (he punched a satellite for Pete's sake...)
2. The "O Thunder" right-arm gatling gun (Beck is lucky to have survived, Wainwright's 2nd megadeus wasn't so lucky... Both these destroyed robots also used bladed weapons, but were still defeated.)
3. The Dorothy-assisted "Final Stage" gun (a tribute to the "big gun/main gun/big weapon" concept, present in many other anime, and other cartoons, too. Although it's been seen before, I still enjoyed it...)

.The Final Negotiator.