The world of undead is great. So some would think that it would be hard to pick one undead to be my favorite, but I say unto you nah for I say that the best Undead is The Death Knight. I think the first encounter I had with the death knight was in the Dragonlance books.
In the 1e game I am working one, I have 3 temples in an underground city. I am thinking about changing 1 of them in to a temple of undead just so I could have the players fight a Death Knights. I don’t think I could even tell you why I like them but there you are.