Yay! I love coming up with this kind of stuff! Let me have a go:
The Vampiric Nightblade
Skulking in the shadows until the perfect time to strike, the Vampiric Nightblade's prey will never see them coming. They are nature's ultimate predators, and their prey is man and mer. Their principle ally is Stealth, the art of being unseen, for the darkness is a vampire's best friend, and they loathe to be seen. Supplementing their already-cat-like covertness are the Illusion spells of muffle and invisibility, with which they are naturally skilled, making it literally impossible for their prey to see or hear them until it is too late. Their predatory charm can also help them to calm their prey before feeding, and their dominating willpower and terrifying visage can induce a maddened frenzy in their foes if they are discovered or outnumbered. Or, they could simply drive their unlucky quarry to succumb to overwhelming fear, giving the vampire the opportunity to relish the pursuit. Their skill with Illusion magic will be so impressive that they can cast their spells stealthily, as they use their abilities to obfuscate the sound and sight of their power from others.
For obvious reasons the Vampiric Nightblade will prefer to go for the throat, up-close and personal, and they are befittingly One-handed blademasters, particularly proficient with daggers, but also skilled with a sword should the situation call for it, for fencing is a noble pursuit, and vampires are noble creatures (they will never use a shield, though, for they are bulky, heavy, and clumsy). But if the choice is between making a kill, and remaining unseen, the vampire will choose remaining unseen every time, and as such they are also skilled at Archery, so that they can remain in the darkness and kill from afar when there is no other choice available. Death from the dark.
Being undead themselves, Vampiric Nightblades are acutely attuned to the dead, and thusly can intuitively call upon the darker Conjuration arts of necromancy, compelling the dead to serve as their thralls. Should the darkness betray them, these undead monstrosities can be raised from among the enemy's own ranks to slay them, to serve as distractions while the Nightblade disappears once more. Their inherent command of, and superiority over, the undead has led to their perverted use of the once-noble school of Restoration, too - while most use it to heal, the Vampiric Nightblade has twisted it to control the undead thralls of others, rightly making them fear the superior vampire, as well as allowing them to heal their own servants as they subvert its healing powers to their own, immortal ends.
Mortal nightblades will often avail themselves of Alchemy, taking advantage of nature's own ability to kill and control so that they can poison and pacify their opponents. It is conceivable that the Vampiric Nightblade may retain this skill from their mortal life, should they have been a nightblade before their accession to superior kin - but they will not use it, at least not against their foes, as they will not wish to taint the blood of their prey with poisons. Instead, their ability to pacify their foes is now inherent, and they are naturally adept at the Alteration spell paralyse, as it is so much easier to drain a mortal that cannot move. And so much fresher... Additionally, their undead nature and heightened durability over mortals will make them seem as though they have stoneskin, which is particularly fortunate as they will usually forgo bulky armour in favour of stealth.
Besides these, the Vampiric Nightblade may retain any number of skills from their mortal lives, but in the pursuit of becoming the perfect predator, they may neglect or abandon them entirely, depending on their interests. But were they skilled at Enchanting in a previous life, this skill may well help them to supplement their already-impressive predatory skills, as well as somewhat compensate for some of the natural disadvantages from which their kind suffers. Given their inherent magical abilities, the Vampiric Nightblade may well take up Enchanting even if they were not previously skilled at it, for precisely these reasons. And besides... they will likely derive a sickly pleasure from not merely using the blood of mortals, but also stealing their very souls to augment their own killing powers! For this reason, the Vampiric Nightblade will likely restrain themselves to using black souls exclusively.
EDIT: As for their equipment, Vampiric Nightblades will use weapons with which they feel attuned; similarly-vampiric weapons will be preferred. Anything that absorbs the health and stamina of their foes will be preferable, though soul trapping abilities would be desirable too. If the Vampiric Nightblade is skilled with Enchanting, they may like to use some of their captured black souls to enchant some Daedric weapons with these abilities, forging personalised weapons that are as dark and malignant as they are. A custom vampiric Daedric dagger, bow, and sword, each with a secondary soul trap ability and manufactured using the bound souls of their enemies, would be a highly prized set of weaponry for the Vampiric Nightblade. If not, the Blade of Woe may be ideal, or you could rely on conjured weapons instead. Ebony weapons would be an acceptable, though less desirable, alternative to Daedric, as they would be camoflaged in the darkness too. Don't use Elven or Glass weapons at all, though. They're frickin' gold/green and sparkly. That's not stealthy.
Their apparel should be lightweight, flexible, and dark in colour. Armour is too bulky, and will restrict movement, but if light enough - such as the Vampire Armour appears to be - it might be acceptable. Dark Brotherhood armour would be good, though dark hooded robes would suit too. Whatever you wear should ideally cover as much of your skin as possible, for obvious reasons.
Everything they wear, from clothing to jewellery, should be equipped with enchantments that attempt to negate the vampire's inherent disadvantages; ideally, their apparel should all work together to steadily regenerate their health and magicka, allowing the Vampiric Nightblade some safety in combat should they be caught off-guard during daylight hours (a real risk, even for the most cautious of vampires, although a risk they should be trying to avoid), and ideally adding some fire resistance too. Again, if they are adept at Enchanting, they can customise it accordingly, again ideally combining these regenerative abilities with resistance to fire magic, or skill boosts that benefit their stealth and illusion attributes, and black souls should be used to accomplish this.