I'm interested in what styles of RP characters you all associate with the new Dawnguard factions; For example, I might personally use a healer/archer character for the Dawnguard and a thief/warlock style character for the vampires. What are your thoughts?

When I heard of Dawnguard, I made a new character who had some of his family killed by a group of vampires, thus developed a burning hatred.

Thats my motivation for joining the Dawnguards

In the last week I made a dark elf who wants to rule the world and destroy all, and a nord who's family were vampire/daedra/witch hunters but got killed by some vampires.

As the CoC/DC descendant, Dragonborn, and Paladin of the Nine, my character will uphold his duty to protecting Tamriel from unholy threats.

With his wife Mjoll the Lioness, and Erandur the priest, Aradal will usher in a glorious new dawn for mankind, as he uses the legendary Auriel's Bow to scour the vampire lords from existence.

My wood elf is currently learning the tricks of the trade as an archer/one handed specialist, he will then be moseying along and stumble along a vamp (most likely in broken fang cave) .
He will then, begin to succumb to his vampiric urges retreating to the woman who helped him become a better archer and his only true friend (Angi). He will, unfortunately for her, feed on her and nearly kill her, at which point he will be so disgusted with his actions that he will do whatever it takes to rid himself of this curse.
Blah, blah, blah, does the quest to get rid himself of his vampirism and will dedicate his life to ridding the world of as many vampires as he can, all the while haunted by his time as a vampire.

Recently made a Imperial, who as a young man was mentored by an experienced vampire hunter after his life and Anvil's were almost ruined by them.

Venturing to make a name for himself he has gone to Skyrim in search of Volkihar vampires described in Immortal Blood. Meridia as his patron and Stendarr as his witness, evil will be hunted down by him till ends of Tamriel. Recently, he contracted Lycanthropy in his journeys with the companions. He feels a battle rage inside as the beast howls to be satisfied yet he is determined to use the curse for good and weapon against evil.

[As soon as he hears of the Dawnguard, he will venture forth to join them]

Gryden, the Nord Warrior that the Scrolls foretold of, is the Champion of Meridia and, regretably, Molag Bol.
Aside from his greedy dealings with the Daedra, only doing their bidding for the powerful items they reward, Gryden wishes to protect his land from any and all evil creatures.
He will join The Dawnguard, destroy their enemies, and will be rewarded with land and title. Fort Dawnguard will be his land, Sir Gryden of the New Dawn being his title.

My Dark Elf is an alchemist (basically a doctor though. He only makes potions, preferably healing ones) and an assassin. Desire to find his sister and passion for his work (both assassinations and being a physician) will probably make him side with the Vampires. Mostly because he sees the kind of semi-immortality as a blessing to perfect his skills and the power as a great way to crush the Stormcloak rebellion and find his separated sister.

My new Nord Witchhunter is a disciple of Arkay and spent his youth as a squire to a group of witchhunters operating in Cyrodil.

He travels to Skyrim to see the land of his ancestry, study at the College of Winterhold, and see what is really going on in the civil war.

Once his adventure in Skyrim stars, he will investigate the rumors he hears about a group of vampire hunters who seem to be recruiting...

My Cyrodiilic vampire, Draken, fled from Cyrodiil after the collapse of the Empire. Not interested in politics as his sister, he seeks to find new purpose in his life. After hearing about a dark prophecy of the Tyranny of the Sun, he seeks to support the vampiric cause. In his point of view, the Dawnguard are evil. He might spare Serana in the storyline.

For my second playthrough, it will be with my Cyrodiilic female vampire, Raven. Her choices will be different.