The two professional mainstream choices are:
Since you are not the photographer, but the graphic artist, you will be more concerned with the layout designs and output rather than the photo workflow. In that regard, I would consider Apple Aperture the better program.
Adobe Lightroom's strength is its integration with Photoshop. It's seamless to go between Adobe Camera Raw and Photoshop. My concern was its lack of good printed album functionality. It may have improved over time, but you'll want to take a look at what Lightroom can (and can't) do with album design and layout.
Apple Aperture’s export options are better than Lightroom's. You can create web galleries and, more importantly, the support for exporting and printing albums is much better. Once you set up your album designs, you can view the photos in a "virtual lightbox" where you can easily swap out combinations of photos to see how they look in your design. Given that you are a graphic designer dealing with common page layouts, this would seem to be the killer feature.
Here is a very recent comparison of the two programs: The Aperture vs Lightroom Shootout.
Try them out for yourself. Both applications have demo versions.