My main character will be siding with the Dawnguard. Level 49 Nord, 100 in every combat skill but archery. He's looking to branch out his knowledge since he's been revealed as the Dovahkiin, so he's been dabbling with bows, as well as stealth, and magic skills.

My Nord Warrior who's a Werewolf (Hopefully i can still help the Volkihar while remaining a Werewolf), my Dunmer Nightblade who's a Vampire (Going with Volkihar), my Argonian Mage who's a Necromage Vampire (Going with Volkihar). Thinking of making a Breton Spellsword to go with the Dawnguard.

I have and its what I rely on when using a Bow xD

Having the ranger perk is pretty fun too, I feel like Legolas

yes. 100% pure Nord, fresh from the Housecarl
9th. i accidentally let it loose (and somehow opened a portal to Oblivion) while trying to fix my microwave with a spork

My Imperial Mage will be joining the vampires for UNLIMITED POWAH and my nord paladin will obviously be wiping the vampire scum off the face of tamriel
My mage is level 81 though so I may need to nock up the difficulty to get a challenge out of the DLC

my female Vampire dunmer mage is going to join the Vampire legion in the DLC.
dawnguards look lame
and i cant wait to highjack there fortress and destroy everyone of them

Dang, 81? how much time did you put into that?..

Dunmer DnD style thief.. I might go Vampire before DLC...

I wonder what effect being a vampire before hand will have on the story...

I'm gonna guess it will be very minimal.

Im going in as a werewolf Altmer warrior with ring of hircine for unlimited transformations. All level points invested into Health and stamina. No offensive magic.

My Nord Barbarian werewolf will be a mutual ally to the Dawnguard. My Dunmer rogue, depends on who pays more. Imperial assassin... Going to take over and become the new vampire lord.

Join me brother, and together, bunnies shall rule the galaxy!

I have a high level Dark Elf who is a bit of a mix of everything except for the light and sneaky character traits who I will unglitch his armor and legitly go through the Dawnguard storyline. (I chose him for the reason that he's a heavy character and for the reason that Dawnguard as well as he aren't/isn't my favorite set, it works well.) For the Vampires, I'll use my other character, my kahjit who is great in light armor and sneak as well as traits to enhance the performance around those areas. (I chose those two for pretty obvious reasons. )

my sword and board khajhit werewolf is going to with dawnguard

and my Breton conjuration Mage that's a vampire is going to side with the vampires althoug I'm deciding which skill to use offensively for this character its either dual weild swords, archery, or destruction on a low difficulty

I'll be taking two characters, one for either side.

My main character aptly named The Outlander: http://skyrim.nexusmods.com/imageshare/image.php?id=87896
A jack of all trades, weakest in mage skills, strongest in warrior and thief skills. He'll side with the Dawnguard.

&

Zaar Bloodsong, entirely inspired by the Dawnguard trailer: http://skyrim.nexusmods.com/imageshare/image.php?id=93117
A powerful Battlemage, strongest in conjuration, destruction and one handed skills. He will become a Vampire.

I'm leaving it all to chance... I'm dice rolling for race, dice rolling for combat style, and as for marriage... Janken with my arch rival: if I lose, I will find the ugliest girl to my taste; if I win, I will find the most beautiful.

of course, my Breton mage that occasionally likes to turn into a werewolf.

I was afraid of that. It will probably be a slight difference in dialogue. Kind of like how talking with a certain member of the Dark Brotherhood is different if you have started the Companions.

Alteration is VERY easy to level up, and the protection spells like Ironflesh and Ebonyflesh will become monumentally important, if you don't want to wear armor
or waste and uneccesay amount skillpoints on health instead of magicka. The Mage Armor and Magic Resistance is also incredibly useful, and something a pure
mage don't want to pass up on. If I were you, I'd use all of the mage-skills, and don't bother leveling up enchanting until late-game since that is the only time
you'll be able to actually surpass the 'good' items you find randomly throughout the world.

As for the OP's question - I've played Skyrim for over 400 hours, but I've NEVER made a sneaky character, let alone a character that had any other interaction
with the Dark Brotherhood other than wiping them out. So I've recently made a new character, a Breton named Aluc Cardienne who's a vampire already. This dude
is going to aid Harkon and his band of Vampire lords.

My already existing Imperial, Tiberius Principius, is going to help wipe them out.

My paladin will be the herald of the Dawn in this darkest of nights

Breton battlemage ftw

Custom shouts would be great for a mod, mayhaps even through a alchemy/enchanting pedestal = SHOUT ALTAR , you could sacrifice human and dragon souls alike to parthaunax!

I'll go through it with my Once-stealthy-but-now-since-hes-lv-81-he-kinda-does-everything Argonian. Siding with the Dawnguard for sure.