It's hard to say.
I don't really know anything about Mortal Wombat and we just declared on them so I'm reserving judgment there. They may yet turn out to be even worse than our C&G opponents.
The Orange Defence Network... sigh. You guys talk about International screwing over their former allies, well they've been at it recently but they learned from the masters, which are the ODN. They're not evil, conniving and manipulative, they just have a tendency to make stupid assumptions which cause their treaties to breakdown. I had front row seats for it during Karma. Int are in the same boat I think: they didn't hate LSF (well I think they do now) they were just really bad allies because of stupidity.
It's hard to rate ODN and International from a military standpoint. I mean, yes, they're pure meatshields as they were among the first counters on the other side, and got pummelled by a huge number of alliances. They are clearly not elite alliances but they never made themselves out to be. Hopefully they know they're just meatshields absorbing damage.
GATO on the other hand are using dove in the worst way I've ever seen. They are apparently trying to intimidate their opponents into giving up, and think they can do this with inadequate warchests and hiding basically their whole midrange... and then they only declared on midrange-heavy opponents. It's really stupid.
So GATO.
Plus GATO has Darth Cyfe, who is third only behind Arexes and Ephriam Grey in the annals of Insane Invicta Haters.