My reason that Evil is always preferred is severalfold:
1) In all the generic hero movies and books and stuff, Good always beats up Evil. Not cool.
2) NO MORALS. Evil can cheat, steal, lie, and do all these other awesome things without any code of honor or civility in the way.
3) Just plain cooler. Dramatic black cloaks, wicked scythes, deadly poisons, and espionage is infinitely more appealing than fluffy white clouds, floaty blobby halos, and old books.