Your character can be of any species of creature imaginable.
Human, angel, demon, werewolf, fairy, vampire whatever your little overactive brain can think of.
But there are some guidelines for the characters,
and they are as follows;
The Good Guys The characters who are (supposed to be) always on the good side.
Angels
They reside with God in Heaven, and fight for the good of humanity....usually. There are a few corrupt angels left in Heaven who help Lucifer's cause from the inside; but for the most part they are self-righteous and very, very powerful.
Hierarchy of Angels:
Archangel (7 of them, 4 of them are elemental archangels)
Seraphim
Cherubim
Thrones
Dominions
Virtues (only 7 of them)
Powers
Principalities
Angels
Note: Archangels weren't always all powerful, they used to be only one step above Angels until Michael brought the Archangels to glory by singlehandedly destroying Lucifer.
There are angels who are born in Heaven who have no true last names, but have a title. The archangels are the Angelus and Sanctus, and the rest of the angels born in Heaven are titled the Dei. Their titles work like last names, such as Michael Angelus or Ai Dei.
Humans who died and became angels keep their original name from earth.
The Middle Men The species of creature that could be on either side.
-Note- every creature MUST have a side... they may change, but they have to be on one.
Humans Mostly the goal of the entire war is to win over the most human souls. Being caught up in the middle is very taxing to the human beings, who have now all joined a side and are either passive; in hiding, or aggressive; in the fight. The passive humans are usually scientists, politicians and wounded refugees while aggressive humans fight all the time.
Elves 
Usually on the side of good, these creatures are cunning, valuable in combat and very opinionated. They are just as likely as vampires to rise quickly through the ranks, and to very high heights. They have a large range of talents, both able to fight in physical combat and become mages.
Werecreatures 
Werecreatueres, such as werewolves and werecats, are believed by most to be guardians of humans- lost or divine souls that must guide their subject through life by following them in animal form throughout their lives. Whether that is for good or ill is, again, up for interpretation. They live primarily in the forests near their side orientation and usually only come out to fight.
Vampires 
Vampires are believed by some to be d**ned souls trapped in humans bodies and allowed to roam the earth- whether to redeem themselves or to further corrupt humanity is up to interpretation. Because of their superior strength and cunning, they are usually high ranking in the organizations of either side; sometimes rising to ranks of almost that of angels or demons.
Fairies 
True creatures of magic, they don't truly belong to this world or dimension. They are skilled spellcasters but poor hand-to-hand warriors. They are by nature secretive, playful and childish. Male fairies, or pixies, blend well with humans because they can change their size at will. The downside is that male fairies have a very limited energy reserve for their magic, and so have to rely on the cunning of their spell and their size in battle. Female fairies, while they can only change their size for short stints of time, are far more powerful than their male counterparts. Their energy reserves are far greater.
The Bad GuysThe characters who are (supposed to be) always on the bad side.
Demons 
The consorts of Lucifer, they reside in Hell- but play alot on Earth. They are much less concerned than the angels in leaving their domain to converse with the humans; humans are closer to a demon's corruptness than an angel's divine nature.
Hierarchy of Demons:
Satans/ Vices (Only 7)
Fallen Angels
Devils
Daemons
Demons
Imps
Damned Souls
The Satans have the title of Diabolus, and were born in Heaven. They are the most powerful Fallen Angels. Other demons who were born in Hell or were low ranking angels who fell from Heaven have the title of Mallori (pronounced :mal-or-eye) Their titles work the same as the titles of angels
Hellhounds The sentinels and guardians of hell, they are direct servants of the Satans.
*Half-Breeds are welcome

(As long as its not like, half-demon, half-angel... be realistic at least)
*Try to keep the good guy/bad guy ratio even
*The mixture of powers is limitless.. except, again it has to be realistic. For instance; an angel is not going to be able to summon hell fire, or kill someone instantly. Demons are not going to have healing powers (since that is associated with white magic) and so on and so forth.
*Only the 4 elemental archangels have total control over an element. The rest is very limited.
*Did I miss a character species that you wanted? Send me a PM and ask for me to add it, and I will consider it!*