Caillou hands down.... I could never, can never, and will never tolerate that brat in my house. (the only cool thing about the show was that he had a friend named Xavier.... my Xavier thought that was neat as its a rare name to hear the few times it made its way on to the tv screen).
I can't dispute Barney as I grew up with him and he wasn't THAT bad.
What annoyed me when my kids were little was the repeats.... but that's what those shows are designed for... take the original Blue's Clues (my favorite by the way), it was designed so that they aired the same episode every day for a week... through repetition is how kids learn from them... it's just SUPER annoying for the Parent and Caregivers to have to hear the same things over and over again.