A place to discuss over which Ainur would win in battles with each other and which one has the most power. But just because a Ainur has more power and a larger army and is more clever, another Ainur might have better physical strength. So you could place the battle in different places and times(some Ainur might be stronger at one point but become later on). Maiar that were corrupted into monsters such as Balrogs, Ungoliant and other evil creatures are counted as deformed and corrupted Ainur. A good battle to start the discussion off: Gandalf vs. Saruman. One might have more power because they served a more powerful Valar, or defeated stronger enimies, or one used to be more powerful than the other, but it changed around. Also the Valar might or taken away more power from one than the other when the Wizards entered Middle-earth(maybe because the Valar did not want Sauron to know that the Wizards were Maiar). Think of different times and places the battle could take place in and who you would think would win in that scenerio.
Well, before Gandalf is resurrected as Gandalf the White, Saruman is probably stronger, although Gandalf (Olorin) is the wisest of the Maia.
After Gandalf is resurrected, we know who is much, much stronger. (Read: permitted to use more strength)
Massively depends upon the situation. A hammer in the ocean would be useless, but Ulmo on land would also be fairly inept. Honestly, it'd be a stalemate and we can't tell who'd come out slightly on top.