A topic which I've run tests with before (long time before), apparently has come back with Apple's Safari for Windows release. Jeff Atwood finds Mac OS X fonts wonky - well, they're certainly soft. Apple has never been too keen on strong hinting, perhaps because it messes inter-glyph metrics in favor of contrast. Windows is wonky in its own way - ClearType has good contrast, but letter spacing is sometimes a bit annoying.

Just for kicks, here's what Fedora 7 with FreeType autohinting and subpixel rendering (equivalent of ClearType) looks like. This is just one of the modes, but the one I personally prefer:

Comparing at 200% rendering to Jeff's examples; Safari/Windows, IE7/Windows, and Firefox/Fedora

I guess it's up to everyone's preferences, but I think Fedora wins this one. Spacing isn't perfect here either (in particular "b est" looks a bit ugly), but overall, contrast is excellent and paragraph spacing is very close to what it would be without hinting.