Straight up, I like Aperture better than Lightroom. The way it works fits my mind better.
However, I've been working with the Lightroom 3 beta lately, because I've been unhappy the with amount of chroma noise in the photos from my new Canon 50D in Aperture 2 (ISO 400 shots). I'm shooting RAW, so this isn't an in-camera conversion problem.
For the 50D, Lightroom 3 Beta's RAW development simply blows away Aperture 2 in the image quality department. It's not even close.
Today (technically, yesterday), Apple announced the long hoped for Aperture 3. I grabbed the trial, and immediately put it through some RAW development tests, hoping that it would equal or better the image quality from Lightroom 3 beta.
Aperture 3 is a solid improvement over Aperture 2 in the image quality department for 50D RAW files. Apple certainly raised the bar.
Unfortunately, the RAW developer in LR3b has already set an even higher standard.
I'll post examples tomorrow. Right now, I'm going to bed disappointed.