ubuntu obviously chooses sharpness over balance (H and E), however osx has virtually every lowercase character heavily aliased, its blurry to the point where its almost 2 shades lighter than its supposed to be and there are individual characters A, u, B, a where it is almost a joke
Ubuntu has similar (but not exactly the same) levels of fuzziness, but the rendering is inaccurate. Character tracking/spacing is the biggest issue, but there are others.
If you look at traditional fonts that are designed for print or general purpose use (e.g. Helvetica, Frutiger, Univers, Myriad, etc.), the accuracy and quality of OS X rendering stands out considerably. There is simply no comparison.. and once you get used to it, the small amount of "fuzziness" that you observe in small point sizes just doesn't bother you anymore.
I use osx every day, I am very used to it, I just prefer ubuntus rendering by quite a long way