So as the title suggests, I have finally come to be tasked with a choice. I never went the vampire route in oblivion, and havent heard much in Skyrim. So, Can you guys give me some pros and cons. this goes for quests as well. What am I missing out on if i join vamps? and I guess what other than VL form am I missing out on if i go DG?

I liked WWF in the sense that you really could forget that you are a werewolf for extended periods of time and there was no real consequence. Is this kind of the same with Vamps?

Depends. If you want better unarmed attacks (khajiit or argonian) and/or want to roleplay as a vampire than go vamp lord as your initial choice. I enjoyed my playthrough as a vamp lord for those reasons.

Best crossbow, armored troll and the ability diwn the line to go vamp lord than go dawnguard

If you get your enchanting up to 100 and could care less about the vampire roleplaying extras i would go dawnguard .

Will serana stay with me if i side with DG? and if so, can i work for Dg then at end go VL ? i kinda want one of there hounds.