Favorite Sigma fight (Megaman X series)

What's yours?

Armored Armadillo because my friend says you can't beat it unless you use Spark Mandrill's gun, and ever since I got the game every time I've played through I've beaten him with my standard X-blaster. He's really bad at that boss fight.

My friend still doesn't believe me that you can.

X4's. The one in X6 was pathetic beyond belief.

X5's was interesting, but I'll always have a place in my heart for the first Sigma fight.