For once, I disagree with the Sweet Setup. Duncan Davidson:
While Aperture and Lightroom are positioned as competitors, they have distinctly different strengths. Aperture’s strength is in its user interface and its organizational tools — it is the best tool for the long-term process of building out collections of finished photographs. However, when it comes to taking a pile of images, selecting the best of them, and then making those look awesome quickly, Lightroom is the better application.
I’ve used both extensively, and I found Lightroom to have a cumbersome interface and a strange workflow. I also found that its tools, while more robust than Aperture’s, could not offset these issues. Couple that with Aperture’s library and super easy “Vault” backup features and I find Aperture to be the better of the two.
But would I recommend it over Lightroom? Probably not. Apple tends to struggle with keeping their pro apps updated. In addition, Duncan Davidson is a photographer, while I am simply some dude on the internet that takes pictures. You should probably take his advice and use Lightroom, but I’ll probably stick with Aperture.