Kevrock I'd draft the next Ryan Zimmerman if I could, too - especially if I knew the guys after him were much worse and had little chance of developing. There's really no way to know, though, because best player available is usually pretty muddled.
If I have to choose between the next Ryan Zimmerman and the next Roy Halladay or Mark Teixeira, I'm probably not going to pick the next Zim b/c I've already got one.
With respect to the Pirates, can't Rendon just be moved somewhere? I don't follow college ball very much and haven't seen him play, but his listed size is on the smaller side 3B. Could he be moved to LF?