I would say go PS3... it makes a great Bluray player, and it is software upgradable. But the best function of the PS3 as others have said is the Media Player. Google "PS3 Media Server"... if you have many videos on your computer, this program will stream them directly to the PS3 in upconverted 1080P. It is amazing the quality of some of the videos after the upcoversion. PS3 will even play streamed HD videos with no problems too. My only issue with PS3 has been the implementation of Subtitles when streaming, but that is not a PS2 issue if you know what I mean... Now with that said, you must have media you want to stream, because if your just playing Bluray, it would not make a lot of sense for just that. Either case, if you get a stand-alone, you better have network access.... Bluray players always seem to update firmware... my Sony Standalone has had 6 updates since Christmas to tweek minor glitches here and there.
Final note, if you go with a Standalone player, check if it supports resume of a Bluray. Sound funny, but I have the base Sony unit, and not only do you have to install a USB thumb drive in it to give you BluRay extras, but there is no support of Bluray resume. You either pause or stop and start over. I personally don't like to pause for long period, so the first time I used my standalone, I was 3/4 finished a movie when the door bell rang, I thought like a DVD player, press stop once, and when I return press play. NO GO, it started over. Now that may be something most do suffer from, but check it out!