I wish we'd had DeAndre Jordan on his rookie contract, but I'm glad we don't have him on his current one.
For me, it's failing to resign Tony Allen on the cheap in 2010. A unit of Rondo, Bradley, TA, Pierce, and KG would be absolutely smothering against nearly any small-ball lineup in the league. And TA would give us another defender to throw at the superstar wings out there. He's a piece we've missed.