Results from ACR with Nikon NEF files have always been pretty good, if not the best, but results with Canon CR2 files were poor.
However, with ACR 6 that’s all changed. Adobe decided that a complete ground up rebuild of ACR was what was required to get back on even terms with the competition and, wow does it make a difference. At high ISOs in particular, Adobe’s RAW processing software is now about the best there is, leaving previous market leaders with a hill to climb.
Although I prefer the Adobe Lightroom 3 interface, the ACR module is exactly the same in Photoshop CS5, so results will be identical. Which is the best Photoshop? To me now, it comes down to the workflow, or interface, and Lightroom 3 wins that hands down. Photoshop CS5 has new features but it, and ACR 6 now look old fashioned in comparison to Lightroom 3.