Based on your brief requirements statement, Aperture is the way to proceed. I've used both Aperture and LR extensively, and Aperture is by far the better software for managing photos.
At the moment, LR might have a leg up regarding processing of RAW photos. But since you have CS5 you have the same RAW processing engine that's used in LR. One caveat--CS5 and it's version of ACR will probably not see updates to accomodate new cameras. There's ways around that (e.g., DNG) but they are a pain. OTOH, Aperture relies on updates to the OSX system to enable processing of images from new cameras, so it will likely support any new camera you might acquire in the future (they can be slow about it, though).
Aperture offers much more than LR when it comes to managing and cataloging photos. IMO, LR is a lousy system for asset management. It is dependent on a folder-based system, has fewer metadata capabilties than Aperture, and the LR developers seem more focused on the RAW processing aspects of their application. As a result many features essential for good photo management have been neglected and some bugs in that area have been around for literally years.
If "the best managment software for my photos" is your primary objective, go with Aperture. But be sure to put in some time understanding it's asset management capabilities before you get too far into it.
BTW, I agree with Butch about a lot of things, but Peter Krogh's The DAM book isn't one of them. I found Krogh's approach way too complicated for what I do (and I shoot over 200,000 images a year), and he is still basing his system for archival storage on optical media, at least based on a quick look of the latest version on-line. I can't recommend it, but see for yourself by exploring the book on-line.
