i personally own both WinDVD 9 Plus (BD) and PowerDvD 9 Plus (BD) . the reason being is that WinDvD 9 needed updating, and the update site never worked for me. between the two, image and sound quality are better in PowerDvD 9. (i have a X-Fi and the Creative Gigaworks 7.1 speaker system) so far i haven't liked the sound quality of any of the free BDPlayers i've tried, but to be honest, its also been a couple years since i tried any of the free ones, so there might actually be something decent out there now.
now, pressing play in PowerDvD keeps giving an alert window that something called TODO crashes. i typically just hit the [x] in the corner to close the alert out. most times the disc loads and plays just fine. sometimes i have to restart powerdvd and press play again, but the 2nd time is always a charm (TODO always seems to crash, and all i know is that it's launched with PowerDVD, but never seems to affect playback outside of the above. i think it has something to do with the online component, but haven't cared enough to extensively research it.)