I went from Aperture 3, to Lightroom 3, back to Aperture 3.
I've always liked Aperture's workflow and organizational tools (and call me lazy, but I liked not having to worry about my own file management), but it was unusably slow and buggy on my new laptop that shipped with Lion, so I took it as an opportunity to try something new and switched to Lightroom for a few months.
Eventually I learned Lightroom's tools well enough that I reached the point where I was getting the same quality of output out of Lightroom as I was out of Aperture. I still never liked the "module" workflow though,
A few updates later, Apple fixed the Lion bugs and Aperture was stable on my new laptop, so I switched back for comfort reasons.
In my experience, they're both capable of about the same quality of output most of the time, though their toolsets are different. The order of operations you take to nail exposure in Lightroom won't necessarily be the same order of operations you take in Aperture.
A few notes on Lightroom from my experience:
- Everyone says Lightroom has way better noise reduction. That is true - Aperture deals well with chroma noise but poorly with luma noise, whereas Lightroom deals well with both. Lucky for me, I don't find luma noise to be as objectionable as chroma noise, and it doesn't really rear its ugly head when I share photos on Flickr or Facebook, or in small prints. Still, this is the biggest thing I miss from Lightroom.
- Lightroom has automatic lens corrections. Aperture needs this badly. Like, yesterday.
- Lightroom has output sharpening, Aperture does not (except for printing) and needs it.
a few notes on Aperture:
- In the last 3.3 update, Aperture's white balance tool gained the ability to white balance off of skin tones. This works impressively well - I've gone back to old pictures I never got a satisfactory WB on, clicked on a patch of skin, and voila.
- Aperture has "edge detect" brushes, and it actually works. It's such a timesaver for me not having to go back with an eraser to fine edges when dodging and burning.
- I prefer Aperture's "Edge Sharpen" brick to Lightroom's "Sharpen" tool.
- Aperture seems to import photos much more quickly than Lightroom, but they're comparable in speed in just about everything else.