I use Aperture for 90% of my photo work, to do all my image sorting and RAW conversions. The default RAW conversions (what you get with the built in profiles and no adjustments) are the best I've found.
I admit that I don't use all of the advanced functions like the light tables (and since I've never used iPhoto I'm not sure what you're getting from Aperture over that program.)
As far a photoshop goes there are so many more functions in PS that it's hard to compare the two, they really are very different programs (but since I've never been happy with the default or auto settings in Camera RAW and I don't want to have to adjust every RAW image I'm converting I've been using Aperture a lot.
But if you really get into digital photography and image manipulation you'll end up with photoshop, it's really an indispensable tool.
The equivalent of Aperture from Adobe is the soon to be released "Lightroom" BTW.