My first _real_ char was an Undead Mage (I played all classes till lvl 15-ish first :P).
So when I had a feel for the game, I went Undead, for the simple fact they Lady Sylvannas is the coolest NPC in the game, and I love her, so Undead was the logical choice for me.
Mage because I've always been a casting class in about every mmo I played.
Now I'm levelling a Blood Elf Paladin, because you can't roll Troll Paladins QQ
Seriously ... Berserking + FoL?! I wouldn't mind that!
And I have a Tauren Druid that's currently collecting dust in Dustwallow Marsh I think, I just wanted a cow tbh.
And my coolest char by far is my lvl 6 Blood Elf Rogue! She has style, and 19 hours /played
I use her to set up my UIs without being bothered by whispers and stuff. :P