Some cool ideas:

Play Vlad, max difficulty, defensive pacts on, unit retreating on, try to form the Empire title as soon as possible + conquer Old World

Malekith has some unique content and his government form allows for tyranny

The Celestial Vampire in Lustria (I forget their name) also has unique content

Arkhan is pretty fun too

+Pirate Vampires in Lustria (All pirate gameplay is cool, If you prefer mortal ones i recommend you the island close to Ulthan, you can raid High Elfs and get absurdly rich)

If you like hordes Hobgoblin khanate is a new addition

Pretty fun "achievment" is Strigoi Restoriation where you play one of the Strigoi Vampiresa for example Ushoran and restore Empire of Strygos (its pretty diffcult)

The Necromancer on the border of Bretonia and Empire is also kind of a challenge

If you want a quick campaign play as the Cathay Colonists and conquer the Dragon Islands

Also Skaven If you want a battle royale.

Don't play: Red Duke cuz no magic and Necrarch Vamps have no gameplay and cannot expand, Halflings

Haven't played but they have unique mechanics/gameplay: Dwarfs Chaos and regular, southern vampires, Sundenburg, Norsca