Dear god , here we go again.
Just like that dude who has a sig along the lines of "every thead on SHH must have a mention of Nolan " , it's the same thing here ...only with ILM or WETA.
EVERY TIME, EVERY TIME someone starts mentioning VFX those 2 companies are the first and only qualified studios out there to handle all the VFX in the world

.
Seriously you can get (one of )the best VFX studio out there and hire some lame director and you'll wind up with horrible VFX.
Look at Digital Domain. Their work in Tron Legacy ( with the exception of the digital face of bridges) was amazing. Ditto Benjamin Button. Why is the VFX in GI Joe rise of the cobra are bad ? Or the Mummÿ 3 ?
Even WETA isn't fool proof. They have Avatar , they have LOTR movies , they have King Kong. But they also have done ERAGON , they've also done Rise of the Silver Sulver and The Day The Earth Stood Still.
Small studios can also deliver some fantastic shots . D9 is a good example of that. Ditto WETA when FOTR came out and Manex FX ( which isn't closed if i'm not mistaken) which won the VFX oscars in 2000 for their work in the matrix.
Get the right director and you don't need to worry about the shots , regardless of VFX studio. SNyder is that kind of guy.
Now look at the practical side of things. I do think that this time around Sony Imageworks won't be the main studio working on Superman. THey're busy with Green Lantern and once that's done , they'll go right into Spider-man. Even with Superman coming dec 2012 , i don't think they'll be able to handle the majority of the shots if they can start working after SPider-man is done ( which will be June-July 2012). But they can do some of the shots.
WETA is busy doing the shots of Tin Tin and is also preparing for Hobbit. You can bet your ass that they will be the only VFX studio working on Hobbit. Hobbit will be a massive undertaking for them, so much so that they won't be able to handle another big project. It happened when they were doing the LOTR movies , it happened during King Kong and during Avatar. Considering that filming is going to start soon on Hobbit and it'll end sometime next year , you can pretty much scratch WETA from your list.
ILM could be a possible contender. Aside Battleship , i don't see any big project which they're working on for 2012.
It's the same with Digital Domain , Framestore CFC etc.