The debate could be between Orc & UD. It really depends on your style and game type.
Orc - Strongest race, it has strongest units, heros, and defense. I think its AA might be its most lacking asset.
UD - Most versatile race overall, whatever it might be lacking in it makes up for with speed and versatility.
NE - Considered the noobs race, I think there just fun, units are not as strong as orc nor as versatile as UD.
HU - The most tactical race IMO, I think any great HU player, has been so from good micro, and strategy.