Let me preface this by saying that I am basing my comparisons on just one of each type of player. The only players I have used are the PS 3 (Blu-ray) and the Toshiba HD-A3 (HD-DVD).
Basically they appear pretty equal in terms of picture quality, so I am making my comparisons just on the basis of the functionality of the players themselves.
I've had my PS 3 since March and I think it works EXTREMELY well as a Blu-ray player. It loads discs very fast, (usually within about 5 seconds) and has many useful features that I like.
1. I like that you can fast forward to x1.5 and still have sound and see subtitles. I often watch foreign movies, but I tend to be impatient, so it's nice to be able to fast forward through the boring parts, but still be able to read what is being said.
2. I like that you can change audio tracks and subtitles "on the fly". Which audio or subtitle track you are currently using is briefly displayed on the screen.
3. I like that you the on-screen display will show things like the bit rate of the video and the audio track, time remaining, etc. This is especially useful to me, because I like to check what the difference is between the compressed and uncompressed audio tracks.
In fact, about the only drawback I can find to the PS 3, is that it doesn't seem to do well in an enclosed cabinet.
I just got they Toshiba A3 yesterday, and I find it very clunky to use. For starters, it takes about 30 seconds from the time you press the power button, before you can even open the disc tray. It's a little bit faster with standard DVD's.
1. When you fast forward on the A3, no sound or subtitles. I find this pretty annoying.
2. For some reason, on the A3 you can't change subtitles on the fly. You have to open the menu and select the subtitles menu. Not such a big deal, but then why is there even a subtitle button on the remote? It doesn't do anything. When you change audio tracks, nothing is displayed on the screen, so you don't know which track you just switched to. Obviously if you hear Spanish, you know you just switched to the Spanish track, but there's nothing on the screen that tells you this.
3. The on-screen display of the A3 is VERY basic. It doesn't give you bit rate or show you how much time is remaining in the movie.
Even more annoying about the A3, is that it reacts VERY slowly to commands. If you press a button on the remote while watching an HD-DVD, it literally takes about 3 to 5 seconds before that command is carried out, (i.e. press fast forward, wait 3 seconds, then it starts to fast forward). This really bugs the hell out of me. Again this is considerably shorter with a standard DVD, but I bought the A3 for HD-DVD's.
Now , I don't know if the A3 is typical of other HD-DVD players, but I think it's a real pain to use. The PS 3 definitely works MUCH better as a high def video player. In the future, I only plan on buying HD-DVD's that I can't get on Blu-ray, (Transformers, Batman Begins, etc.). If this is how all HD-DVD players function, then I think this is just another factor in the HD video war that gives Blu-ray the advantage. However TONS of people ran out and bought Toshiba players over the last couple of days, so this battle is getting very interesting.