Mine is actually Sakura. She grabs too much of the limelight from time to time. And unless she's getting all medical on some poor sap, she's acting like a total tool stroking Sasuke's ungrateful ego at Naruto's expense. It's almost sickening, really.
Granted, most of these flaws were apparent pre-Shippuden, but even still. In my personal opinion, she was almost forgettable, afterward. As if she was there just wasting space and perfectly good oxygen.