The name Alien obviously does not limit players to play as just alien, it would clearly limit peoples experience of the game.
I just know that I (and probably many others) prefer alien as a side, and would home in their eliteness on the alien tactics. Playing as a roaring Tyrant i something that many other games cannot offer.
Another factor of knowing how to be the best at playing alien is that you know the weeknesses of humans, therefore when you decide to take up your gun, you know where to shoot and how to act against the different alien forms, and level of player. At the end of the day predicting your enemies level of skill is the main element to a skilled player.
For example knowing the perfect theory of a game doesn't make you the best, but the interpretation of who you play against and how to tempt them to your advantage remains the ultimate element. That is the aim of the clan [Alien] and it is what my members(3 and growing...!!) and I will learn to master!
Plus you know, being able to communicate well ingame and having decent people to talk to and the weekly pub crawls...