Befor the invasion, Right now, No limits. Which team is gonna win.
So far it seems Ozai's angels. Zuko has proven himself time and time again to be enough to take Aang by himself which is Gaang's major player. Sokka, now more skilled with a sword isn't nearly as skill as the others and will be fried in cross fire from Zuko and Azula battling someone else. Katara is the biggest threat if she can get close enough to water. But the girl with the pressur points could end her bending. Leaving Toph and Aang, which as I said Zuko could take Aang by himself and so could Azula.
Sokka is a better opponent now than from the Chase. He'll surprise Mai and Ty Lee for a second or to. Aang's problem is that he fights like an Airbender, very passively and often evading and figthing to disarm not to defeat. Aang is a bit more confrontational and stronger due to earthbending but he needs some furiosity and aggression that comes along with firebending. Zuko isn't a master firebender yet but he is closer than he was in Book One. Katara is a very dangerous opponent when she wants to be, especially at night, more specifically a full moon, or near a large body of water. Toph would be very hard to fight in open combat, Azula and Zuko never battled her before and Ty Lee not really much about her.