Obviously he is not going to name anyone on current roster though.
During a Q&A discussing how teams prepare for the draft, Kevin McGran of the Toronto Star asked Toronto Raptors president and general manager Bryan Colangelo who he would pick as his worst selection.

"I had a draft selection in Phoenix, No. 22 [in 2002]. I picked a kid named Casey Jacobsen from Stanford and Tayshaun Prince went 23rd. I missed because we had Shawn Marion and felt Prince was more or less a duplication. But I made it up by taking Amar'e Stoudemire at No 9. And then a kid Paul Millsap went 47th [in 2006]. And at 35, we took P.J. Tucker. That was a mistake."

Ironically, Tucker currently plays for the Suns and he's part of their rotation this season.

Colangelo has been in charge of the Raptors since 2006 and his first round picks include Andrea Bargnani, DeMar DeRozan, Ed Davis, Jonas Valanciunas and Terrence Ross. Those five players are still with the Raptors.