... but compare Phyrexian Walker to Wall of Wood. Both creatures are 0/3. One is 0cc while the other 1cc and the 0cc creature can attack. Also, like the Ornithopter, the Phyrexian Walker is a great target for a Cursed Flesh, Rancor, Unholy Strength, or any other really good 1cc Enchant Creature spell. Also, as a second turn drop after a god draw of Ritual plus whatever, it's perfect as a Twisted Experiment target. If all else fails, it's a good wall, but Shield Sphere is much better in that capacity.
Over all, Shield Sphere is my favorite with the Kobolds in a close second.