For me, my biggest mistake was taking '11 Plank. I went cheap early (cheap versions of Wynn, Sutton, Caminiti). I missed all Plank's good seasons. I had my eye on 1905 so I could also use Rube Waddell. With those two plus 2002 Pedro and Lowe, I'd have my 4 SP's all set. But I didn't want to take the 10M cap hit so early, so I decided to take 69 McMahon (for Marichal), then the cheapest Plank available (7M of suckiness)... just to lock down C, 2B, 3B (Cochrane, Collins, Baker).
As it turned out, 05 Plank went really late in the draft. And there were other decent teammate choices at 2B (i.e., a couple of nice Jackie Robinson seasons) and 3B (George Brett, Morgan Ensberg, Eric Chavez).
The other mistake I made was passing Yount's last really good OF season by taking a mediocre Ozzie Smith instead. Sure enough, Yount went right after that, and I was kicking myself. At least I now have a $4.6M defensive replacement.
I will post my roster / stats a bit later.