Never ever hire incompetent people who are beyond help, no matter how nice. What's the point? You are running a team that needs to perform. It's not a charity or a social club. By keeping incompetent people you send a horrible sign to the rest of the team and the team will crack under the stress.

Reject the notion that you can only find jerks to get the competency you need. Just be sure they are willing to work for the team. Some will be real nice, the rest will learn to get along. Make expectations very clear up front and be willing to fire for bad behavior.