I do prefer Aperture over Lightroom and the main reasons for preferring Aperture is because of the below mentioned features:
Not trying to argue with your choice... different tools for different people, but some of the features listed below actually do exist in Lightroom... so just for accuracy and for people who have not yet made up their mind...
1. It has capability for organization by project
Lightroom uses Collections (instead of Albums) and Collections Sets to organize Collections and Smart Collections. So, yes Lr can organize by projects. As well you can save a print job and reprint that at will.
2. It has a option for managing files
Lightroom also allows for managing files once the images are imported. You can use what Aperture calls "Referenced" images or you can have the images moved by Lightroom into it's default file structure.
3. They had Multiple book printer options
True. By default Lr only has one book option, though others are available with plugins I believe. I keep a copy of Aperture and iPhoto around specifically for this feature. Note that Aperture and iPhoto have different options from each other, even though they are both Apple products.
4. It is much less dependency on Photoshop
Lr has as much dependency on an external editor, Ps or otherwise as Aperture. Though it is nicely integrated with Ps should one wish to use Ps as the optional external editor.
5. Can be used for White balance using skin tones
Yes. Lightroom does not have a way to white balance on skin tones. I hadn't realized that Aperture had this feature... the only other application I was aware of was Capture One v7... which is an even more powerful editor (though not as strong at organizing images) than either Aperture or Lightroom.
Like I said...not trying to get you to change you mind... just wanted to set the record straight for anybody who is still looking at a DAM.
Cheers