Which Tv tuner is better?

I use a Hauppauge WinTV 850 USB TV tuner that has record features. It explains in the set up that the amount of space you allot on the hard drive directly affects the recording quality. It also allows you to record in formats other than MPEG-2. I have yet to record with it and haven't used Diamond hardware, but Hauppauge has good support, including a free software upgrade when I switched to Windows 7. Hope this helps.