In terms of PQ(picture quality) Blu-ray is a Blu-ray you won' notice a difference now if it's PQ of a DVD that's when there's a difference how well is the PQ on the PS3 vs Oppo J is more qualified to answer that question since he owns both. In terms of audio quality I doubt there's a difference unless your using the analog outputs on the Oppo then this would be a point in their favor.
IMO if you want a stand-alone BDP just to cut down on the wear and tear of the PS3, also a lower power consumption vs the PS3 then I would suggest looking in the Panny models which would cost less than the Oppo and offer many features which are the standard among most models. Here is one I have been looking into for myself the
Panasonic DMP-BD85 has pretty much everything except the ability to play DVD audio or SACD.