I understand your point - I was not a fan of Noble until halfway through her tenure. I think she is one of those characters one has to take on their own terms - a homebody, and an obnoxious one, who longs for something more. My sympathy for her might stem from the fact that I know many people like her from my own childhood - but I can understand she might grate on you. I liked the fact that she was really not too bright, but she worked her inventory with everything she had. She was emotionally a basket case, but carried on anyway and just sucked it up and dealt with it (after blubbering, of course). The fact that she needed a good shaking from time to time made it more rewarding when she pulled it out and did something great. That, and her insights (re: sick days, for example) came from her (very limited) experience, not raw brainpower.
Is it wrong of me to enjoy someone truly average trying so hard and succeeding to a level that Pipers' and Freemans' characters achieve with much less effort and drama? Probably. Maybe it is like watching the Special Olympics - it isn't about being the fastest or best in the world, it is about living up to ones greatest potential, and putting out maximum effort, even if competing in a field one cannot possibly be world-beating in. I think that is it, for me.
I will agree that Rose was the best rendered companion of the new series, and IMHO the Eccleston Doctor was the best of the new series, from a Doctor-companion character standpoint.