Darko Milicic and Hasheem Thabeet have to be tops in the worst picks ever made. They are a complete waste of space on the court and don't even remotely try to get better.
Stoudemire has been injury prone too his whole career. in fact he hasn't done anything since Yao retired. but at their peaks, they're about equal. Yao had a bigger impact on the defensive end but also had problems staying effective and on the court due to poor stamina. on offense, Yao had problems with fronting while Stoundemire was unstoppable in Suns' pick n roll offense.