
I would have to say Kiryu.
2 REASONS WHY
#1: Remember in Godzilla against Mechagodzilla, Kiryu had the Absolute Zero Cannon, which I believe, almost killed Godzilla 2000 twice in the movie. I believe the cannon freezes objects and turns into a snow-like dust.
#2: Also in Godzilla Against Mechagodzilla, Kiryu is a clone of Godzilla 2000.

The sentimental person inside me wants to say Gigan. I simply like Gigan way more as a monster than Kiryu/MechaGodzilla.
However, if I'm being objective, Kiryu would win. He has way more ranged weaponry, which would allow him to implement an effective kiting strategy.
Furthermore, if we use their respective battles with Godzilla as reference points, Kiryu overall has been a much tougher opponent vs Godzilla than Gigan has been, implying that Kiryu/Mechagodzilla is higher up on the monster food chain.

why are you calling godzilla from G x MG godzilla 2000, and then calling kiryu a clone of godzilla 2000
1. GxMG and SOS has no connection with godzilla 2000
2. Kiryu is made of the bones and DNA of the ORIGINAL 1954 godzilla.

kiryu would win hands down. even without the weapons he is still quite the power house

I'm too lazy to research anything so can't we all just agree Gigan is more awesome and leave it at that? :P

Gigan is more awesome :-)
I haven't saved up the dough for any S.H. Monster Arts figures....but when/if I do, Gigan is the first one I plan to buy (after getting one of the Godzilla figures of course)
You'd think for being built/modified by an advanced alien race he would have received a more decked out arsenal of weapons.......alas...he did not :_( :-( QQ

Kiryu got this. In Final Wars Gigan's head got blown off two times by Mothra and Godzilla.

kiryu basically tied with Godzilla in both films that he was in whereas Gigan just got destroyed multiple times or ran away.
As much as I used to like Gigan he's a pretty weak monster in the series.