i haven't read the replies, but as a user of both can offer some insight:
I began with Aperture, and used it for years. I absolutely loved it, and never thought I would switch - then I discovered Lightroom.
Lightroom is hands down the better of the two. Although Aperture offers some things that Lightroom doesn't, it's not worth choosing over LR in my opinion.
Lightroom's noise reduction and clarity sliders are worth choosing it alone in my opinion, but it depends on what type of shooting you do. I have a 5d3, and I take full advantage of its high ISO capabilities. While it shoots amazing pics at ISO 6400, it looks MUCH better with some noise reduction. When using Aperture, I often times have to use plug-ins to match LR's abilities and that leaves me with massive TIFF's. Also, the new clarity slider is miles ahead of Aperture's definition slider. While it can be heavily abused to make photos look like total crap, it's magical for many situations - especially black and white images.
There are tons of other things that LR dominates Aperture in, but those are my favorites.
Now, the reasons for choosing Aperture are simple for some people. It integrates well with OSX. You can choose photos for your background without having to export them, and you can stream them on your AppleTV with ease. It also allows you to paint in any effect you can apply globally - this is something that LR lacks. However, LR allows you to paint in a group of effects - something that Aperture lacks.
So, to answer your question - if the user is not going to worry about massive amounts of editing and wants to have better integration with their operating system, go with Aperture. If you want the most options, and the best functions, go with LR.
I know this is personal to many people, but I have to say that LR is objectively the better of the programs in terms of "power use," but I can see the argument for Aperture to some people.
Also, you have to remember that Adobe focuses almost exclusively on image editing, whereas Apple is a computer/phone company first and foremost. Making image processing programs is a way to lure you into buying a Mac.