They are really two quite different devices aimed at different target audiences. You need to consider which fits your needs best.
The PS3 has been highly recommended as a Blu-ray player because in the first couple of years of Blu-ray it was the most cost effective option. However, stand alone Blu-ray disk (BD) players have started to change the equation. The Oppo BDP-83 is arguably the best BD player on the market, and certainly the best for the price IF you value video quality of both DVDs and BDs, and the ability to play CDs, SACD, DVD-A etc in one "universal" player.
On the other hand, if you want to play games, as well as CDs, SACDs, DVDs and BDs (at lower quality than the Oppo), and have a basic home media player the PS3 is the choice.
If all you want is to play audio and video disks and get the best sound and video the PS3 is a poor choice. It uses 6X as much electricity as most stand alone players, is a mediocre DVD upscaler (an important consideration for those with DVD collections), has styling that doesn't fit into anyone's HT system and requires a specialized remote (e.g. it's not compatible with most universal remotes). On the positive Sony have supported the PS3 with frequent firmware updates, something not all BD player manufacturers have done (That said Oppo have an excellent track record in this regard too).
On the other hand the Oppo is both more expensive and less flexible, while an excellent universal disk player it is best suited to those who value it's capacity to generate top notch video and audio suitable for audiophiles and videophiles.
Personally, I'd buy the Oppo over a PS3 in a heartbeat ... but I have no interest in games, and if I want a media player I'll buy one. However, the PS3 offers more capability for the $$ so depending on your priorities you must choose.
Hope that helps.