This is just one man's opinion, but I would only recommend a stand-alone player if you really need the analogue audio outputs. So basically, it depends on what your sound system is capable of handling.
If you have an older receiver that does not have HDMI inputs, then it would be worth while to go with the Panasonic DMP-BD55 Blu-ray player. I must stress here though, even if your receiver does have HDMI inputs, they MUST be capable of accepting a 5.1 and/or 7.1 PCM audio signal. There are some lower cost and/or older receivers that have HDMI inputs, but those HDMI inputs cannot accept 5.1/7.1 PCM audio. Being able to accept 5.1/7.1 PCM audio is
critical, so double and triple check, just to make sure
So, to summarize:
1) If you have a receiver that has HDMI inputs that CAN accept 5.1/7.1 PCM - then I would strongly recommend the PS3 as your Blu-ray player. The PS3 is MUCH faster when it comes to loading discs, navigating menus and accessing any BD-Live (internet) content. The PS3 also provides reference quality Blu-ray video output. There is zero concern about its video quality
It's also a pretty darn good DVD upscaling player too. Not the tip top of the world, but certainly no slouch and better than many of the inexpensive (or even many of the expensive) upconverting DVD players out there. The PS3 gets frequent updates and it is, by far, the most commonly tested player for compatibility issues. Where other players sometimes have compatibility issues with certain Blu-ray discs (sometimes, it's new DRM, sometimes it's BD-Java, sometimes it's BD-Live - but basically, most stand alone players seem to run into compatibility issues with a few rare discs from time to time, while the PS3 almost always works because the studios test extensively to make sure their discs will play on the PS3). The PS3 also fully decodes ALL of the new HD Audio formats. It outputs these formats in "raw" 5.1 or 7.1 PCM via HDMI, which is why it is vital that your receiver be able to accept 5.1/7.1 PCM via HDMI.
2) If your receiver cannot accept 5.1/7.1 PCM via HDMI (either because it has no HDMI inputs, or because the HDMI inputs that it does have are not capable of handling 5.1/7.1 PCM), then the DMP-BD55 becomes the best choice.
Of the stand-alone players, the DMP-BD55 is likely the head of the pack. It certainly does not load BD-Java titles nearly as quickly as the PS3, but so long as you're willing to wait for that initial load, the rest of the experience is pretty much equal to the PS3. BD-Live still navigates a bit slower, but overall, it isn't too bad. Video quality is right on par with the PS3 and all audio is handled by the DMP-BD55, so you're all set for everything that Blu-ray can deliver
