Another big advantage of Aperture's Curves tool is that you can have multiple Curves adjustments. If you use this strategically you can save yourself lots of work in the long run. To add a second (and third, fourth, fifth and so on) Curves adjustment, from the cog pop-up menu at the top right of the Curves adjustment panel, choose Add New Curves Adjustment.
An example of why you might want to do this is as follows. If you want to add contrast to your image, but you also want to use curves to adjust the colors, rather than doing it in one adjustment, you can do your brightness adjustment in one curve and do the color adjustment in the other. This separates the two processes mentally and will allow you to visualize the adjustments a bit easier. This, in turn, will make it easier to make adjustments.
Another reason is if you need to apply one set of adjustments to one part of an image and one set of adjustments to another. As Curves can be brushed in, you can use multiple...