Just the visceral and grotesqueness of option 2 is just a depiction of physical prowess, really pushing the vampire bat form to the upper limit of what's even possible before going in to some wight territory, and it is awesome for sure, however i personally don't really feel it matches up with the voice over description we got narrated by Chris, it's an enhancement of the vampires abilities, not just physical, but also magical, and it just "feels" wrong, when i look at the second Option I do not get the sense of a creature that could possible use Magic / Blood Magic, it just looks like a physical damage dealers.
Keep in mind this is the option we get to decide how the Bloodmoon Vampire Bat Form will end up looking like, and with that in mind i don't really view it as a contest, Option 1 is in my mind not only the clear winner (the correct choice) it's the only choice that fits the description, so even though Option 2 does look awesome i personally don't view it as a good fit for the Bloodmoon Vampire Bat Transformation.
And that is why i cast my vote for Option 1.