Horde, specifically Forsaken because I always choose the most monstrous looking race I can. Undercity is dark and quite honestly my favorite city next to Stormwind or the Gilneas capital (name escapes my mind). The abominations, the music, Sylvanas, (at the time) the Dreadlord, the flying bats, and it had the coolest place for magic classes (specifically Warlocks) so I felt so happy there. Tirsifal Glades is also very nice looking to me.
I also played Undead in WC3 so they were a favorite from then. They can hold their breath underwater which is very cool (redundant for a warlock but still), they can eat people, and they just aesthetically look cool to me. Also their dance and laugh is amazing. If I ever wanted to look normal, I had the blood elf orb :3
Also because Forsaken are the superior race and they will blight nuke everyone, starting with the disgusting creatures known as Gnomes, followed by the delicious tasting Tauren steak beasts.