Not the worst, but top 5 for sure.
The only reason KOC has appeared to have any success with the Jazz is because he made one great move in trading for Deron Williams and has been fortunate enough to have a hall-of-fame juggernaut coaching the team. Without Jerry Sloan, KOC would look embarrassingly bad as a GM.
--Has screwed up every first round draft pick he's had since taking over except for Williams (kinda hard to screw up the 3rd pick when you have Deron Williams and Chris Paul on the board) and Brewer.
--Decided it was a good idea to pair two of the worst defending big men in the league together in the front court and pay them gajillions of dollars to let guys half their size score at will in the post.
--John Amaechi
--Made the masterstroke of bringing back Greg Ostertag
--Thought Carlos Arroyo was a starting quality PG in the NBA
--Thought Raul Lopez was better than Tony Parker (maybe he was before the injuries, but prolly not)
--Thought Kris Humphries was better than Al Jefferson
--John Amaechi
--Let Mo Williams walk for nothing
--Drafted two psychopaths in a 5 year span (Kirk Snyder and Deshawn Stevenson)
--Extended Okur
--John Amaechi
What has he done right?
--Drafted Deron Williams
--Drafted Ronnie Brewer (no longer on the team for financial reasons)
hmmm...... oh yea
--Traded for Kyle Korver
--Drafted Paul Millsap
--Eventually gave up on John Amaechi
And that's about all I can think of. I'm sure there's much more on both sides, but that's all I could think of off the top of my head. All in all, it's been a pretty depressing era since KOC took over. He's had a few small successes and one big one (Deron), but for the most part it's been a flood of one incompetent decision after the other.