im trying to lvl up one of my characters so it can be a death knight and im wondering which class is best and what race.
im not asking how im asking what race should it be and what class should it be??

whatever class u enjoy the best.but for me i have a level 76 death knight worgen

I myself like the Draenei death knight for their Gift of the Naaru. Death Knights are a class of their own. If you roll up a character up to level 55, you can not make that character a death knight, you need to roll up a death knight after you get a character up to level 55. I have 6 death knights on one server,

The Death Knight itself is a class. Maybe you are talking about talents?

Death Knights are unlocked at level 55.

You make a new character to be a Death Knight, which starts out at level 55. It can be any race, any faction.