I have the 6600 and love it. Really easy to use, camera and video clips look pretty goodfor a phone too. E-mail function is nice, so when on holidays you can take a picture and e-mail it straight away to your mates back home to p**s them off (managed to do this quite well from Oz)
Also you can add various apps to it such as a gameboy emulator, Opera video editing tools and more. Syncs nice with Outlook too, updating address and calendar on both the phone & outlook.