OSX font rendering is optimized for high ppi displays (128+ ppi). If you try to look at screenshots of OSX font rendering on low-ppi displays (i.e. typical Windows laptop with 15" display at 1366 x 768) it's going to look incredibly fuzzy.
On the other hand, ClearType is optimized for low-ppi displays. If you try to view text rendered with ClearType on a high ppi display (128+ ppi) it will look incredibly thin because ClearType attempts to force straight font lines into a single row or column of pixels which is incredibly thin at such a high ppi. That's the very thing that makes ClearType fonts look much crisper on very low ppi displays.
tl;dr OSX font rendering is much more readable on 128+ (or even 220) ppi displays.
I think this comes down to personal preference. I am on a 24 inch screen with 1080 lines and I still prefer reading text in OS X to Windows on it. On my shabby laptop, not so much.
On the other hand, ClearType is optimized for low-ppi displays. If you try to view text rendered with ClearType on a high ppi display (128+ ppi) it will look incredibly thin because ClearType attempts to force straight font lines into a single row or column of pixels which is incredibly thin at such a high ppi. That's the very thing that makes ClearType fonts look much crisper on very low ppi displays.
tl;dr OSX font rendering is much more readable on 128+ (or even 220) ppi displays.