Ive actually owned the O2 for a while and still own a S9. the O2 is amazing for playing video, but absolutely nothing else. the interface is terrible, the sdk is worthless, and audio playback is anything but smooth and intuitive. battery life was so-so, nothing amazing but not terrible either. the sd card integration is practically nonexistant, which makes it useless for music as well. videos from the sd card seemed to work fine. as great as the video playback was, it did fail on me about 2 weeks after owning it. a few shows that i tried playing ended up as green screens, corrupted the files and crashed the player. i put up with a ton of corrupted files on my archos 605 and refused to do so with the O2 so i shipped it returned it immediately.

The S9 i received last week. as of now its wonderful. you can barely tell that the interface is even by the same company, its that much better. the lack of expansion doesn't allow you to have too many videos, but if you don't have much music that shouldn't be too big of an issue. the screen is straight up amazing. much more responsive than the O2 and the oled is just beautiful. sadly it doesn't support as many video formats, but as most of my shows and movies are in avi it doesn't matter. and despite what the specs say, it can support 480x720 resolution with no difficulty. bluetooth playback is crystal clear, but that largely depends on your headset. i have the Samsung SBH-600 and quality is just as good as wired headphones. also, battery life is almost scary good. i listen to music pretty heavily and im still on my first charge from a week ago.

what you shouldnt take into consideration is widgets and sdks. neither is anything special, mainly just thrown in to say, hey look what we have. what is available is fairly buggy and slow.

basically, the s9 wins hands down, with exception of format support. if your files are not avi you may run into trouble. supposedly the S9 supports wmv but i have yet to try it.

another option you might consider is the archos pmps and imts. they support a ton of formats, have very simple interfaces, and have fairly decent battery life. there's no bluetooth which is a bummer. ive actually owned several, and my only complaint is occasionally music files would become corrupted. this may have been fixed by now, i don't know.

other than that i have yet to find another pmp with decent format support. good luck!