10) Necrophiliac free, if you know what I mean.
9) Gnome cuteness > all.
8) None of our races have to bear the brunt of endless "bull by the horns" or "bullcrap" jokes.
7) We have PvP gods (Pally's) while all you get are wimpy Shamans.
6) We smell better. Not only do Trolls and Orcs seldom bathe, but those Undead can't be too fragrant either.
5) We don't have to watch people eat corpses. Honestly, I wonder how the rest of the Horde even maintains their appetite.
4) We get all the good patches of land. You have... what, swamps and wastelands?
3) We actually win all the wars in the previous games.
2) We have all the hot women. All the ones the Hordies have have either tusks or horns, or are (un)dead.
And the #1 reason) Dwarf tossing.
Go Alliance!