Aperture FTW
Why?
It does everything I need it too in very slick way (especially since 2.0 came out)
I love the integration with mobileme's web-albums
It LOOKS way better/slicker than Lightroom IMHO
Other than that, I already used aperture when LR came out so I never really bothered trying that extensively as Aperture was doing everything I needed it to very well (and still does).