When it comes to ease of use, PowerDVD and WinDVD are almost identical. The only problem that I had with WinDVD was that the graphic menu was a little too small for my liking, sometimes making it hard to hit the little buttons. Features supported are just about on par with PowerDVD.
Intervideo's WinDVD was the only player that could truly rival, and marginally surpass, PowerDVD's visual quality. The picture was crisp and clear, and exhibited no banding or artifacting. Pixelation was also at a minimum except while running at full screen -- this is totally forgivable though, as the software is actually stretching the 720x480 movie to fit an 1152x856 resolution 19” monitor.
Hardware motion compression is fully supported in this release of WinDVD, but can sometimes act up if you aren't using your video card's reference drivers. While using hardware motion compression there were no visual quality problems like the ones that occurred in PowerDVD, so I'm willing to bet that the green lines that appeared in PowerDVD while enabling motion compression were a PowerDVD-specific problem.
Unfortunately WinDVD's audio support is not as good as that of PowerDVD's. Support for LFE is present, but support for individual sound cards is lacking in four-speaker mode as well as Dolby Digital 5.1 (through S/PDIF). WinDVD also claims that it has support for DTS S/PDIF Pass Thru, but I was unable to test this feature.