Dawnguard.
You can still become a Vampire Lord, you have access to the Crossbows/Bolts and the Huskies have better stats than the Death Hounds.
If however you plan on being a Vampire/Lord, then maybe side with Harkon due to some accessories that boost VL form ect, but honestly even then it's just not enough to make me side with them... They were the first faction I chose and came to regret it once I played through the Dawnguard side... Vampire side felt very unfinished.
Also, since you are on the PC, http://www.nexusmods.com/skyrim/mods/28235/?, because I guarantee you that you will get sick of NPCs dying from attacks. There is also one for http://www.nexusmods.com/skyrim/mods/23906/? too