If its a straight choice between 900 and 735, I would only go for the 735 if mp3 playback is important to you, otherwise 900 has to be the choice. But i would agree that the 905 is better still, it even has mp3!
Is the 735 new or secondhand? If it isn't new or it has been used as a demo model, you can check the hours its laser has clocked. I wouldn't get it if it has more than a couple of hundred. The 735 was a great player, but it had some laser burnout issues.